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

Soluble CD23 and interleukin-1 receptor antagonist in human asthmatics following antigen challenge

Two postulated intrinsic anti-inflammatory mechanisms in asthma include the low affinity IgE receptor, or CD23, and interleukin 1 receptor antagonist (IL-1ra). We investigated the role these mediators play in the asthmatic response by measuring local levels in human asthmatics before and after segmental allergen challenge and examined the effect of inhaled corticosteroids on soluble CD23 and IL-1ra levels. Ten subjects underwent bronchoscopy at baseline and 24 hours after antigen challenge. Prior to challenge and every 12 hours afterward subjects received beclomethasone 252 microg or placebo. Fluid was analyzed for sCD23 and IL-1ra using ELISA immunoassays. Eosinophil percentages significantly increased at 24 hours following antigen challenge. sCD23 levels were generally undetectable at baseline and increased significantly following antigen challenge. IL-1ra levels increased 28-fold in the late-phase response. Beclomethasone significantly reduced the late-phase eosinophil percentage at 24 hours compared with placebo but did not attenuate late-phase sCD23 or IL-1ra levels. Our data showed a significant rise in the levels of two mediators thought to play an important role in the attenuation of the asthmatic response. The finding that steroid treatment did not enhance these levels suggests that this may be an independent approach to asthma therapy that should be investigated.

Allergen-mediated modulation of CD23 expression is interferon-γ and interleukin-10 dependent in allergic and non-allergic individuals

BACKGROUND

CD23 plays an important role in IgE regulation. The modulation of CD23 expression during specific immunotherapy (SIT) has been described previously. In the present study, we investigated in detail the effects of complete birch pollen allergen extract (BPA) on CD23 expression of peripheral blood mononuclear cells (PBMCs) in vitro.

METHODS

PBMCs from 14 birch pollen-allergic (bp-allergic) patients and eight non-bp-allergic controls were stimulated with IL-4 and increasing doses of BPA. CD23 expression on monocytes and B cells was measured by flow cytometry; sCD23 release and the levels of IFN-gamma and IL-10 secretion were determined by ELISA. To analyse the mechanisms on CD23 expression in more detail, neutralizing anti-IFN-gamma and anti-IL-10 antibodies were added to IL-4 and BPA-stimulated cultures.

RESULTS

IL-4 induced CD23 expression on B cells and on monocytes and sCD23 release in the bp-allergic and non-bp-allergic groups. The addition of BPA to IL-4-stimulated PBMC decreased CD23 expression significantly and dose-dependently on B cells in both groups. CD23 expression on monocytes was also decreased in both groups after the addition of BPA, but higher doses were required in the non-bp-allergic population. IL-4-induced sCD23 release was also significantly decreased after the addition of BPA. IFN-gamma and IL-10 were induced by BPA in both the bp-allergic and non-bp-allergic groups. The addition of neutralizing anti-IFN-gamma antibodies increased CD23 expression on B cells, which were stimulated with IL-4 and BPA, but had no effect on monocytes, whereas the addition of anti-IL-10 antibodies increased CD23 expression on monocytes but not on B cells.

CONCLUSION

These data indicate that early immunological effects like down-regulation of CD23 on B cells and monocytes, which are observed during SIT are dose dependent, mediated by IFN-gamma and IL-10 and seem not to depend per se on the sensitization state of an individual.

Alteration in the production of IL-10 and IL-12 and aberrant expression of CD23, CD83 and CD86 by monocytes or monocyte-derived dendritic cells from atopic dermatitis patients

Atopic dermatitis (AD) is characterized by the presence of Th2-type cells in the skin infiltration as well as in the peripheral blood, although a predominant infiltration of interferon-gamma (IFN-gamma)-producing cells is also reported in the chronic skin lesions of AD. Recently it has become clear that the development of Th1 or Th2 is strongly influenced by factors produced by the antigen presenting cells (APCs). To clarify whether APCs from AD patients play a favorable role in the differentiation of Th2 cells, we compared the production of cytokines and the expression of co-stimulatory molecules by monocytes (MOs) and monocyte-derived DCs (MoDCs) after stimulations with various reagents between 13 AD patients and 13 age-matched healthy controls. We examined their production of IL-1 beta, IL-10, IL-12p40, and IL-12p70, and their expression of CD23, CD40, CD54, CD80, CD83, CD86 and HLA-DR. We stimulated them with superantigens, lipopolysaccharide (LPS), agonistic anti-CD40 antibody, phytohemagglutinins (PHA), IL-1beta/TNF-alpha, IL-4, or IFN-gamma. The following results were obtained (1): IL-10 production was significantly enhanced in AD MOs after LPS stimulation. In contrast, IL-12p40 production was significantly lower in AD MOs than in HC MOs after a variety of stimulations (2). IL-12p40 was also significantly lower in AD MoDCs after LPS stimulation (3). The induction of CD23 with IL-4 was significantly higher in AD MOs. and finally (4), AD MoDCs augmented the expression of CD83, CD86, and HLA-DR less significantly than HC MoDCs after anti-CD40 Ab stimulation. These data indicate that AD APCs show some responses different from those observed in HC APCs after several stimulations, such as LPS, IL-1 beta/TNF-alpha, IL-4, or anti-CD40 Ab, and that these responses might play a role in the polarizing process of helper T cells into Th2 cells as recognized in AD patients.

The CD23b promoter is a target for NF-AT transcription factors in B-CLL cells

CD23 is atypically highly expressed in various chronic diseases, including B-CLL, lupus erythematodes and rheumatoid arthritis. Its expression can be further enhanced by interleukin 4 (IL-4). We have shown before that in B-CLL cells nuclear factor(s) of activated T cells (NF-ATs) show permanent nuclear localization and therefore constitutive transcriptional activity. Here we identify CD23b promoter as a novel target for NF-AT factors in B-CLL cells. The CD23b promoter contains two NF-AT binding sites to which NF-ATp and NF-ATc factors bind with high affinity. Mutations introduced into these sites abolished NF-AT binding and impaired the promoter activity, as did cyclosporin A (CsA), an inhibitor of nuclear transport of NF-ATs. Furthermore, we show that IL-4-induced transcription factor STAT6 cooperates with NF-ATs in the induction of the CD23b promoter activity. These results show that the CD23b promoter is a target for NF-AT factors and suggest that the cooperation between NF-AT and STAT factors might be one of the molecular mechanisms responsible for high-level expression of CD23 on the surface of B-CLL cells.

Proteases produced by activated neutrophils are able to release soluble CD23 fragments endowed with proinflammatory effects

Polymorphonuclear neutrophils (PMNs) are the major source of proteolytic activities involved mainly in tissue injuries observed in chronic inflammatory disorders. High levels of soluble forms of CD23 (the low-affinity receptor for IgE) were found in biological fluids from these patients, and recent reports focused on a CD23-mediated regulation of inflammatory response. In this context, we show here that co-culture of activated PMN with CD23+ B cells resulted in a drastic release of soluble CD23 fragments from the cell surface. This cleavage was inhibited by serine proteases inhibitors, including a1-antitrypsin. We next demonstrated that purified human leukocyte elastase or cathepsin G efficiently cleaved membrane CD23 on B cells with a high specificity. Soluble fragments released by serine proteases-mediated CD23 proteolysis stimulated resting monocytes to produce oxidative burst and proinflammatory cytokine without any co-stimulatory signal. This work strongly supports the idea that the capacity of PMN-derived proteases to release soluble forms of CD23 participates in the inflammatory process mediated by these cells.

Interleukin-10 and the interleukin-10 receptor

Interleukin-10 (IL-10), first recognized for its ability to inhibit activation and effector function of T cells, monocytes, and macrophages, is a multifunctional cytokine with diverse effects on most hemopoietic cell types. The principal routine function of IL-10 appears to be to limit and ultimately terminate inflammatory responses. In addition to these activities, IL-10 regulates growth and/or differentiation of B cells, NK cells, cytotoxic and helper T cells, mast cells, granulocytes, dendritic cells, keratinocytes, and endothelial cells. IL-10 plays a key role in differentiation and function of a newly appreciated type of T cell, the T regulatory cell, which may figure prominently in control of immune responses and tolerance in vivo. Uniquely among hemopoietic cytokines, IL-10 has closely related homologs in several virus genomes, which testify to its crucial role in regulating immune and inflammatory responses. This review highlights findings that have advanced our understanding of IL-10 and its receptor, as well as its in vivo function in health and disease.

Anti-inflammatory cytokines in asthma and allergy: interleukin-10, interleukin-12, interferon-gamma

Interleukin-10 (IL-10) is a cytokine derived from CD4+ T-helper type 2 (T(H2)) cells identified as a suppressor of cytokines from T-helper type 1(T(H1)) cells. Interleukin-12 (IL-12) is produced by B cells, macrophages and dendritic cells, and primarily regulates T(H1) cell differentiation, while suppressing the expansion of T(H2) cell clones. Interferon-gamma (IFN-gamma) is a product of T(H1) cells and exerts inhibitory effects on T(H2) cell differentiation. These cytokines have been implicated in the pathogenesis of asthma and allergies. In this context, IL-12 and IFN-gamma production in asthma have been found to be decreased, and this may reduce their capacity to inhibit IgE synthesis and allergic inflammation. IL-10 is a potent inhibitor of monocyte/macrophage function, suppressing the production of many pro-inflammatory cytokines. A relative underproduction of IL-10 from alveolar macrophages of atopic asthmatics has been reported. Therapeutic modulation of T(H1)/T(H2) imbalance in asthma and allergy by mycobacterial vaccine, specific immunotherapy and cytoline-guanosine dinucleotide motif may lead to increases in IL-12 and IFN-gamma production. Stimulation of IL-10 production by antigen-specific T-cells during immunotherapy may lead to anergy through inhibition of CD28-costimulatory molecule signalling by IL-10s anti-inflammatory effect on basophils, mast cells and eosinophils.

Interleukin-10 and the Interleukin-10 Receptor

Interleukin-10 (IL-10), first recognized for its ability to inhibit activation and effector function of T cells, monocytes, and macrophages, is a multifunctional cytokine with diverse effects on most hemopoietic cell types. The principal routine function of IL-10 appears to be to limit and ultimately terminate inflammatory responses. In addition to these activities, IL-10 regulates growth and/or differentiation of B cells, NK cells, cytotoxic and helper T cells, mast cells, granulocytes, dendritic cells, keratinocytes, and endothelial cells. IL-10 plays a key role in differentiation and function of a newly appreciated type of T cell, the T regulatory cell, which may figure prominently in control of immune responses and tolerance in vivo. Uniquely among hemopoietic cytokines, IL-10 has closely related homologs in several virus genomes, which testify to its crucial role in regulating immune and inflammatory responses. This review highlights findings that have advanced our understanding of IL-10 and its receptor, as well as its in vivo function in health and disease.

Increased expression of CD23 (Fc(epsilon) receptor II) by peripheral blood monocytes of aids patients

Monocytes expressing the Fcepsilon receptor II (CD23) play important roles in inflammatory and allergic immune responses. We found that peripheral blood monocytes of AIDS patients express increased levels of CD23, compared with monocytes of healthy HIV-1-seronegative individuals (controls) (p < 0.05). We compared expression of monocyte CD23 with expression of monocyte Fcgamma receptors (CD16, CD32, CD64), plasma/serum levels of IgE (also IgM, IgG, IgA), and Th1 (IFN-gamma) and Th2 (IL-4, IL-10) cytokines. We found that monocyte CD23 expression directly correlated with monocyte CD16 expression (p < 0.01, R = 0.58), which was also increased in AIDS patients; there was no correlation with CD32 or CD64 or with soluble factors in plasma/serum (i.e., IgE, IL-4, IL-10, and IFN-gamma). Interestingly, despite the known ability of IL-10 to downregulate monocyte CD23 expression, plasma IL-10 levels were increased in these AIDS patients compared with controls (p < 0.05). We thus evaluated the effect of AIDS and control plasma or rhIL-10 to regulate CD23 expression by monocytes in cultures (24 hr) of healthy human cells +/- treatment with anti-IL-10R blocking antibody. We found that anti-IL-10R blocking antibody treatment had no effect on monocyte CD23 expression in cultures containing AIDS plasma, but increased monocyte CD23 expression in cultures containing control plasma (p < 0.05) or rhIL-10. In conclusion, the identification of increased monocyte CD23 expression in AIDS patients may further characterize the aberrant activated phenotype of monocytes during the immunopathogenesis of HIV-1 disease. Further, monocyte CD23 expression does not appear to be suppressed by the IL-10-enriched environment in AIDS.

Nitric oxide augments release of chemokines from monocytic U937 cells: modulation by anti-inflammatory pathways

Nitric oxide (NO) appears to act as an inflammatory mediator on monocytic cells. Exogenous NO augmented release of chemokines from human promonocytic U937 cells and peripheral blood mononuclear cells. Pharmacological strategies aiming at modulation of NO-induced release of interleukin-8 (IL-8) were investigated in U937 cells in detail. Release of IL-8 was down-regulated by transforming growth factor beta2 (TGF-beta2), by the protein tyrosine-kinase inhibitor genistein, and via rises in intracellular cyclic AMP, generated by prostaglandin E(2), rolipram, pentoxifylline, forskolin, or dibutyryl-cyclic AMP. In addition, incubation with the synthetic glucocorticoid dexamethasone or suppression of activity of p38 mitogen-activated protein (MAP) kinases by SB-203580 modulated release of IL-8. Activation of p38 MAP kinases was confirmed by the demonstration of an augmented appearance of phosphorylated p38 in the presence of NO. The present data suggest that exposure to exogenous NO resembles activation of U937 cells by proinflammatory stimuli. The anti-inflammatory cytokine TGF-beta2, as well as anti-inflammatory or immunosuppressive agents such as genistein, pentoxifylline, rolipram, dexamethasone, and SB-203580 modulate inflammatory, chemokine-inducing actions of NO.

Increased interleukin-10 and macrophage inflammatoryprotein-1α release from blood monocytes ex vivo duringlate-phase response to allergen in asthma

BACKGROUND

We determined the effect of late-phase responses to allergen challenge of mildly allergic asthmatic patients on the expression and release of the cytokines IL-10 and MIP-1α from peripheral blood monocytes.

METHODS

Sixteen mildly allergic asthmatics were exposed to increasing concentrations of allergen aerosol. Nine demonstrated an early response alone (single responders), while seven had an early followed by a late response (dual responders). Monocytes were isolated from venous blood before and 24 h after allergen challenge, and placed in short-term culture for determination ofIL-10 mRNA expression by reverse-transcription polymerase chain reactionand protein release. MIP-1α protein release was measured byradioimmunoassay.

RESULTS

IL-10 mRNA expression was significantly higher in dual responders than early responders alone, for unstimulated monocytes or for monocytes exposed to lipopolysaccharide or IL-1β. In addition, the release of IL-10 and MIP-1α from monocytes of dual responders was also enhanced.

CONCLUSIONS

Circulating monocytes are primed to release more of the cytokines, IL-10 and MIP-1α, in dual but not in single responders, at 24 h afterallergen. They may contribute to allergen-induced inflammatory responsesin the airways.

Interleukin-10 is localized to and released by human lung mast cells

BACKGROUND

Mast cells control the local inflammation by producing many kinds of cytokines. Interleukin (IL)-10 is one of the important cytokine that upregulate or downregulate inflammation.

OBJECTIVE

The aim of this study is to ascertain whether IL-10 is produced from human lung mast cells by cross-linkage of high-affinity Fcepsilon receptors (FcepsilonRI).

METHODS

Mast cells were purified using affinity magnetic selection with mAb YB5.B8 (> 93% pure). Mast cells were precultured with human myeloma IgE (3 microg/mL) for 16 h and then washed, and stimulated with anti-IgE in the presence or absence of recombinant human stem cell factor (rhSCF). We have studied the production of IL-10 by using reverse transcription-PCR, enzyme-linked immunosorbent assay and immunocytochemistry.

RESULTS

We found that human lung mast cells were immunocytochemically stained with anti-IL-10 mAb after IgE-dependent stimulation. The activation of mast cells via FcepsilonRI enhanced the intensity of the IL-10 mRNA signal. Anti-IgE (1 microg/mL) induced a median IL-10 release of 301.7 (7.8-1532.4) pg/106 mast cells/24 h. In contrast, mast cells released only a small amount of IL-10 in the absence of anti-IgE. This difference was statistically significant (P = 0.02, n = 11).

CONCLUSION

Our findings indicate that human lung mast cells are capable of producing IL-10 in response to IgE-dependent stimulation.

Critical role of CD23 in allergen-induced bronchoconstriction in a murine model of allergic asthma

CD23-deficient and anti-CD23 monoclonal antibody-treated mice were used to investigate the role of the low-affinity receptor for IgE (CD23) in allergic airway inflammation and airway hyperresponsiveness (AHR). While there were no significant differences in ovalbumin (OVA)-specific IgE titers and tissue eosinophilia, evaluation of lung function demonstrated that CD23-/- mice showed an increased AHR to methacholine (MCh) when compared to wild-type mice but were completely resistant to the OVA challenge. Anti-CD23 Fab fragment treatment of wild-type mice did not affect the MCh-induced AHR but significantly reduced the OVA-induced airway constriction. These results imply a novel role for CD23 in lung inflammation and suggest that anti-CD23 Fab fragment treatment may be of therapeutic use in allergic asthma.

Upregulation of FcepsilonRI on human basophils by IgE antibody is mediated by interaction of IgE with FcepsilonRI

BACKGROUND

IgE is now known to upregulate the expression of FcepsilonRI on human basophils. It is not known which receptor on basophils mediates this process of upregulation.

OBJECTIVE

We sought to determine whether galectin-3, FcepsilonRII (CD23), or FcepsilonRI were involved in the upregulation of FcepsilonRI by IgE.

METHODS

The role of galectin-3 was examined by measuring the influence of alpha-lactose on upregulation. Basophils were examined for expression of FcepsilonRII (CD23) by flow cytometry and messenger (m)RNA expression. Functional discrimination between binding to FcepsilonRII or FcepsilonRI was examined through the use of mutant IgE-Fc fragments or anti-FcepsilonRII antibody.

RESULTS

Upregulation of FcepsilonRI on basophils in the presence of IgE was not altered by coincubation with alpha-lactose, eliminating a role for galectin-3. Basophils were not found to express FcepsilonRII, as determined by flow cytometry with enriched basophil preparations or RT-PCR with highly purified basophil preparations. A mutant of the Fc fragment of IgE (IgE-Fc), which binds to FcepsilonRI with a greater than 10-fold lower affinity than IgE or wild-type IgE-Fc but exhibits no change in affinity for FcepsilonRII, allowed us to distinguish between the functions of the two Fc receptors. The mutant (R334S; Henry et al 1997) was required at about 30-fold higher concentration than the wild-type IgE-Fc for the same stimulation of FcepsilonRI expression on basophils, thus excluding a role for FcepsilonRII in the response. In addition, treatment of basophils with anti-FcepsilonRII antibody (MHM6), which is known to be competitive with IgE, had no effect on the expression of FcepsilonRI or the ability of IgE to upregulate expression of FcepsilonRI.

CONCLUSION

Collectively, these data indicate that IgE interacts with FcepsilonRI to upregulate its expression on human basophils.

Mechanisms of IL-10 Production in Human Microglia-T Cell Interaction

IL-10, a cytokine with important anti-inflammatory properties, is generated within the CNS during neuroinflammation. The mechanism for its production is poorly understood. Since infiltrating lymphocytes come into close proximity with the macrophage-like cells of the CNS, the microglia, we have used an in vitro human microglia-T cell coculture system to address the mechanisms of IL-10 production. We demonstrate that microglia or activated T cells alone secrete negligible amounts of IL-10, but that their coculture results in significant IL-10 production, which was effected by both cell types. IL-10 generation was cell contact dependent, and treatment with anti-CD40, CTLA-4-Fc, or anti-CD23 decreased the IL-10 content in microglia-T cell cocultures. The combination of anti-CD40 and CTLA-4-Fc reduced IL-10 levels to the negligible amounts seen with T cells or microglia in isolation. By also measuring TNF-α levels, specificity of cytokine regulation was observed; while anti-CD40 and CTLA-4-Fc reduced IL-10 and TNF-α levels, anti-CD23 did not affect TNF-α while attenuating IL-10 generation. Anti-very late Ag-4, which decreased TNF-α levels, did not affect IL-10. These results implicate the CD40, B7, and CD23 pathways in IL-10 production following microglia-T cell encounter and have relevance to the regulation of an anti-inflammatory response within the CNS.

Production of chemokines and proinflammatory and antiinflammatory cytokines by human alveolar macrophages activated by IgE receptors

BACKGROUND

The alveolar macrophage (AM) expresses the low affinity IgE receptor and has the ability to produce not only several proinflammatory cytokines (TNF-alpha, IL-1, IL-6) but also antiinflammatory cytokines (IL-1 receptor antagonist [IL-lra], IL-10), chemokines (IL-8, monocyte chemotactic protein-1 [MCP-1]), and macrophage inflammatory protein-1alpha (MIP-1alpha).

OBJECTIVE

The aim of this study was to evaluate the capacity of the AM from patients with allergic asthma and control subjects to produce chemokines and antiinflammatory versus proinflammatory cytokines after activation by IgE receptors and to define the role of CD23 in this activation.

METHODS

AMs were collected by bronchoalveolar lavage from 13 patients with allergic asthma and 14 healthy subjects. Adherent AMs were activated either by the successive addition of IgE and anti-IgE or by monoclonal mouse IgG anti-CD23 or by a control monoclonal mouse antibody. TNF, IL-1beta, IL-1ra, IL-10, IL-8, MCP-1, and MIP-1alpha levels were evaluated in supernatants of AMs incubated for 18 hours and in some cases after 4 hours of incubation.

RESULTS

Activation by IgE and anti-IgE antibodies significantly increased the production of TNF, IL-1beta, IL-8, MCP-1, MIP-lalpha, and IL-10 in both control subjects and patients with asthma, whereas the increase for IL-1ra was only significant for the control subjects. Whereas F(ab) fragments of anti-CD23 antibodies inhibited IgE plus anti-IgE-induced cytokine production, activation by monoclonal IgG anti-CD23 antibodies reproduced the effect of IgE immune complexes. At 4 hours, the secretion of proinflammatory cytokines was increased by activation by IgE receptors, in contrast to antiinflammatory cytokines. In addition, analysis of the balance between proinflammatory and antiinflammatory cytokines showed that IgE-dependent activation largely favored the proinflammatory cytokines, particularly in patients with asthma.

CONCLUSION

IgE-dependent activation by the FcepsilonRII receptor upregulates the synthesis of both chemokines and antiinflammatory cytokines in addition to proinflammatory cytokines. However, AMs from patients with allergic asthma may promote airway inflammation after activation by IgE receptors through its preferential effect on proinflammatory cytokines.

Nitric oxide production and nitric oxide synthase type 2 expression by human mononuclear phagocytes: a review

Images

CD23 and allergic pulmonary inflammation: potential role as an inhibitor

CD23, a receptor for immunoglobulin E, is expressed at increased levels in asthmatic and atopic individuals and has been associated with disorders characterized by chronic inflammation. Using an established murine model, we employed several complementary strategies to investigate the role of CD23 in allergic pulmonary inflammation and airway hyperresponsiveness (AHR). Specifically, these approaches included the modulation of CD23 function in vivo by administration of anti-CD23 monoclonal antibody (mAb) or Fab fragments to wild-type mice and the analysis of CD23-deficient mice. Administration of anti-CD23 mAb, but not anti-CD23 Fab fragments, produced attenuation of pulmonary inflammation, AHR, and CD8(+) T-cell activation. On the basis of a model that the anti-CD23 mAb transduces, whereas the Fab fragment inhibits, CD23 signaling, these results suggest that CD23 negatively regulates pulmonary inflammation and AHR. This hypothesis is supported by our observation that CD23-deficient mice developed increased inflammation and AHR after sensitization and challenge with allergen. Together, these results indicate that CD23 negatively regulates pulmonary inflammation and airway hyperreactivity.

Binding of anti-CD23 monoclonal antibody to the leucine zipper motif of FcepsilonRII/CD23 on B cell membrane promotes its proteolytic cleavage. Evidence for an effect on the oligomer/monomer equilibrium

In the present study we have compared the binding of two monoclonal antibodies to CD23, EBVCS1 and mAb25, which recognize the stalk and the lectin domain, respectively, on the CD23 molecule. At 4 degreesC, EBVCS1 binds to about 10% of the receptors recognized by mAb25 on the B cell surface. At 37 degreesC, whereas mAb25 reaches its maximal binding within a few seconds, EBVCS1 requires 60 min to bind to the same extent. Stabilization of the oligomeric structure of CD23 with IgE strongly affects in a dose-dependent fashion the number of binding sites seen by EBVCS1 but not the t1/2 to reach them, suggesting that EBVCS1 binds to the coiled coil region through an allosteric mechanism. EBVCS1 rapidly down-modulates the membrane CD23 expression with a coincident increase of CD23-soluble fragments in the culture medium, an effect that is inhibited by IgE. In contrast, mAb25, as well as IgE, protects CD23 from proteolytic cleavage and stimulates its endocytosis. These results suggest that EBVCS1 unravels the coiled coil structure of CD23, rendering it more susceptible to proteolytic attack. This supports the oligomeric model proposed previously (Gould, H., Sutton, B., Edmeades, R., and Beavil, A. (1991) Monogr. Allergy 29, 28-49). The biological significance of these observations is discussed.

Recombinant human granulocyte-macrophage colony-stimulating factor triggers interleukin-10 expression in the monocytic cell line U937

GM-CSF is a cytokine with pleiotropic biological activities and is increasingly used in clinical trials. The present study demonstrates the ability of recombinant human granulocyte-macrophage colony-stimulating factor (rGM-CSF) to induce elevation of interleukin-10 (IL-10) mRNA and protein production in the monocytic cell line U937. As shown by a semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), IL-10 mRNA increases up to 10 times when stimulated with rGM-CSF (100 U/ml) compared to nonstimulated control cells. Maximal IL-10 mRNA expression occurs at 6 h and remains high for 2 h. Thereafter IL-10 mRNA is downregulated and reaches basal level at approximately 24 h. IL-10 protein was measured by ELISA. The protein yield is dose-dependent on the rGM-CSF concentration. Combined stimulation of U937 cells with both GM-CSF and TNF-alpha results in an additive elevation of the IL-10 protein yield. Application of a neutralising antibody against TNF-alpha revealed that GM-CSF induces IL-10 expression independently from TNF-alpha. By using a luciferase reporter gene it was shown that rGM-CSF enhances IL-10 promoter activity 2-3-fold in a transient transfection assay.

Langerhans cells may trigger the psoriatic disease process via production of nitric oxide

Psoriasis is a skin disease that appears to result from a dysfunction in the normal mechanism(s) that regulates wound healing. The Langerhans cell is a specialized epidermal macrophage that may instigate wound healing via production of nitric oxide and epidermal growth factor. Here, Vera Morhenn suggests that, whereas precise coordination of the synthesis of these two substances regulates normal wound healing, a disturbance of this regulation could lead to psoriasis.

Interleukin-10 and interleukin-4 inhibit intracellular killing of Leishmania infantum and Leishmania major by human macrophages by decreasing nitric oxide generation

The host response to Leishmania infection is regulated by a specific pattern of local cytokine production. We investigated the effect of interleukin (IL)-10 and IL-4 on the leishmanicidal activity of human macrophages (M phi). As with L. major, intracellular killing of L. infantum by human M phi was obtained following ligation of surface CD23 or cell treatment with interferon-gamma (IFN-gamma). This leishmanicidal activity required nitric oxide (NO) generation by activated M phi, and it was partially mimicked by cell treatment with chemical NO donors. Addition of recombinant human IL-10 or IL-4 to CD23 mAb or IFN-gamma decreased L. infantum and L. major killing by infected M phi. IL-10 was more potent than IL-4 in inhibiting the leishmanicidal activity of human M phi. Inhibition of Leishmania killing by IL-4 and IL-10 correlated with decreased NO generation from M phi, and was reversed when exogenous NO was added to cell cultures. Therefore, IL-10 and IL-4 down-regulate leishmanicidal activity of human M phi, in part by inhibiting NO generation by these cells.

Cytokine stimulation of T lymphocytes regulates their capacity to induce monocyte production of tumor necrosis factor-alpha, but not interleukin-10: possible relevance to pathophysiology of rheumatoid arthritis

Previous studies in the laboratory have shown that the pro-inflammatory cytokine tumor necrosis factor (TNF)-alpha plays a pivotal role in the pathogenesis of rheumatoid arthritis (RA). The mechanisms involved in regulating monocyte/macrophage cytokine production are not yet fully understood, but are thought to involve both soluble factors and cell/cell contact with other cell types. We and others have previously demonstrated that T cells activated through the T cell receptor/CD3 complex induce monocyte TNF-alpha production by contact-mediated signals. In this report, we investigated further whether T cells activated by cytokines in the absence of T cell receptor stimulation also regulate monocyte cytokine production. T cells were activated in an antigen-independent manner using the cytokines interleukin (IL)-15 or IL-2 alone, or in combination with IL-6 and TNF-alpha. Subsequently, T cells were fixed and incubated with monocytes. Fixed, cytokine-stimulated T cells induced monocytes to secrete TNF-alpha in a dose-dependent manner, but did not induce secretion of IL-10, a potent endogenous down-regulator of TNF-alpha and other pro-inflammatory cytokines. Stimulation of monocyte TNF-alpha was markedly inhibited when T cells were physically separated from monocytes within the tissue culture well, confirming that T cell contact is necessary. T cell acquisition of monocyte-activating capacity was shown to be dependent on the period of cytokine stimulation, with T cells activated for 8 days more effective than T cells activated for shorter periods. Addition of interferon-gamma or granulocyte/macrophage colony-stimulating factor to the T cell/monocyte cultures enhanced T cell induction of monocyte TNF-alpha by threefold and ninefold, respectively. The results from this model of cognate interaction suggest that cytokine-stimulated T cells, interacting with macrophages in the rheumatoid synovial membrane, may contribute to the continuous excessive production of TNF-alpha observed in the RA joint, and to the imbalance of pro-inflammatory cytokines over anti-inflammatory cytokines.