Regulation of cytokine production by soluble CD23: costimulation of interferon gamma secretion and triggering of tumor necrosis factor alpha release

CD23 can negatively regulate B-cell receptor signaling

CD23 has been implicated as a negative regulator of IgE and IgG antibody responses. However, whether CD23 has any role in B-cell activation remains unclear. We examined the expression of CD23 in different subsets of peripheral B cells and the impact of CD23 expression on the early events of B-cell receptor (BCR) activation using CD23 knockout (KO) mice. We found that in addition to marginal zone B cells, mature follicular B cells significantly down regulate the surface expression level of CD23 after undergoing isotype switch and memory B-cell differentiation. Upon stimulation with membrane-associated antigen, CD23 KO causes significant increases in the area of B cells contacting the antigen-presenting membrane and the magnitude of BCR clustering. This enhanced cell spreading and BCR clustering is concurrent with increases in the levels of phosphorylation of tyrosine and Btk, as well as the levels of F-actin and phosphorylated Wiskott Aldrich syndrome protein, an actin nucleation promoting factor, in the contract zone of CD23 KO B cells. These results reveal a role of CD23 in the negative regulation of BCR signaling in the absence of IgE immune complex and suggest that CD23 down-regulates BCR signaling by influencing actin-mediated BCR clustering and B-cell morphological changes.

Soluble CD23 levels are inversely associated with atopy and parasite-specific IgE levels but not with polyclonal IgE levels in people exposed to helminth infection

BACKGROUND

Protective acquired immunity against helminths and allergic sensitisation are both characterised by high IgE antibody levels. Levels of IgE antibodies are naturally tightly regulated by several mechanisms including binding of the CD23 receptor. Following observations that helminth infections and allergic sensitisation may co-present, the current study aims to investigate the relationship between the soluble CD23 (sCD23) receptor, parasite-specific IgE responses and allergic sensitisation in people exposed to the helminth parasite Schistosoma haematobium.

METHODS

A cohort of 434 participants was recruited in two villages with different levels of S. haematobium infection in Zimbabwe. Serum levels of the 25-kDa fragment of sCD23 were related to levels of schistosome infection intensity, allergen (house dust mite, HDM) and schistosome-specific IgE, total IgE and skin sensitisation to HDM.

RESULTS

sCD23 levels rose significantly with schistosome infection intensity but declined significantly with schistosome-specific IgE levels. Furthermore, sCD23 levels were negatively associated with skin sensitisation and IgE reactivity against HDM, but showed no relationship with total IgE.

CONCLUSION

The results are consistent with the suppression of parasite and allergen-specific IgE levels by sCD23. Further mechanistic studies will determine the relevance of this potential regulatory mechanism in the development of helminth-specific immune responses in atopic individuals.

Detection of serum soluble markers of immune activation in rheumatoid arthritis

The mutual correlation among soluble CD4 (sCD4), soluble CD8 (sCD8), and soluble CD23 (sCD23) has not yet been studied in patients with rheumatoid arthritis (RA), although previous studies have demonstrated that certain soluble markers of immune activation are elevated in RA. Thus, we examined this correlation based on the serum levels of sCD4, sCD8 and sCD23, and that of their levels with other serum markers such as immunoglobulin (Ig) subtypes (IgG, IgM and IgA), IgM-rheumatoid factor (IgM-RF) and C-reactive protein (CRP) in 25 RA patients, sCD4 was not elevated, whereas both sCD8 and sCD23 increased in RA patients compared with the healthy controls; a majority of RA patients, in particular, showed a high sCD23 level. The level of sCD23 showed a correlation with that of IgM-RF, but not with those of IgG, IgM, IgA and CRP. Importantly, a high level of sCD23 was not always accompartied with that of sCD8. The independent change between sCD23 and sCD8 levels was also observed in a one-year follow-up study of the two RA patients. These findings indicate that B cells might be generally activated in RA, whereas T-cell activation in variable in each patient with RA, suggesting that sCD23 is a more indicative marker for the immune status of RA patients than sCD8 from the clinical aspects.

Upregulation of ADAM8 in the airways of mice with allergic bronchial asthma

Recent microarray analyses revealed that a disintegrin and metalloproteinase (ADAM) 8 (ADAM8; also called CD156) is one of the asthma candidate genes. However, the function of ADAM8 and its localization in the airways are still poorly understood. In the present study, the changes in the expression and localization of ADAM8 in the airways of a mouse model of allergic bronchial asthma were investigated. Male BALB/c mice were sensitized and repeatedly challenged with ovalbumin antigen to induce asthmatic response. After the final antigen challenge, mRNA and protein expressions of ADAM8 were elucidated by quantitative RT-PCR and immunohistochemistry. The mRNA expression of ADAM8 in the airways was significantly increased in this animal model of asthma compared with naive animals. Immunohistochemical examinations revealed that ADAM8 was located in airway epithelia, airway smooth muscles, and infiltrated cells (mainly macrophages) into lung parenchyma. A distinctly stronger immunostaining of ADAM8 was observed in these airway cells of the repeatedly antigen-challenged mice compared with those of the sensitized control animals. An upregulation of ADAM8 in the airways might be involved in the pathogenesis of airway inflammation and/or hyperresponsiveness, characteristic features of allergic bronchial asthma.

Clipping, shedding and RIPping keep immunity on cue

Exposure to infectious agents elicits defense mechanisms that necessitate a timely immune response. The immediate delivery of essential cues for immune activation is provided, in part, by proteolytic processing. A large repertoire of molecules orchestrates the activation, migration, and effector function of immune cells. The diversity of this repertoire matches well with the broad array of substrates that can be cleaved by proteinases, and many of these substrates are proving to be essential for proper immune-cell function. Here, we discuss how two specific classes of metal-dependent proteinases, the matrix metalloproteinases and the disintegrin metalloproteinases, have consequences well beyond classical cell-matrix and cell-cell interactions and motility, and we review their roles in immune-cell maturation, clonal expansion, and cytotoxic functions.

Expression of ADAMs and their inhibitors in sputum from patients with asthma

ADAMs (a disintegrin and metalloprotease) constitute a family of cell surface proteins containing disintegrin and metalloprotease domains which associate features of adhesion molecules and proteases. ADAMTSs (a disintegrin and metalloprotease with thrombospondin motifs) bear thrombospondin type I motifs in C-terminal extremity, and most of them are secreted proteins. Because genetic studies have shown that ADAM-33 gene polymorphisms are associated with asthma, we designed this study to assess mRNA expression profile of several ADAM and ADAMTS proteases in sputum from patients with asthma and to investigate the relationship between expression of these proteases and asthma-associated inflammation and airway obstruction. mRNA expression profile of selected ADAM and ADAMTS proteinases (ADAM-8, -9, -10, -12, -15, -17, and -33; ADAMTS-1, -2, -15, -16, -17, -18, and -19), their physiological inhibitors TIMP-1 and TIMP-3, and RECK, a membrane-anchored MMP activity regulator, was obtained by RT-PCR analysis performed on cells collected by sputum induction from 21 patients with mild to moderate asthma and 17 healthy individuals. mRNA levels of ADAM-8, ADAM-9, ADAM-12, TIMP-1, and TIMP-3 were significantly increased, whereas mRNA levels coding for ADAMTS-1, ADAMTS-15, and RECK were significantly decreased in patients with asthma compared with control patients. ADAM-8 expression was negatively correlated with the forced expiratory volume at the first second (FEV(1)) (r = -0.57, P < 0.01), whereas ADAMTS-1 and RECK expressions were positively correlated to FEV(1) (r = 0.45, P < 0.05, and r = 0.55, P = 0.01, respectively). We conclude that expression of ADAMs and ADAMTSs and their inhibitors is modulated in airways from patients with asthma and that these molecules may play a role in the pathogenesis of asthma.

Expression of ADAMs and their inhibitors in sputum from patients with asthma

ADAMs (a disintegrin and metalloprotease) constitute a family of cell surface proteins containing disintegrin and metalloprotease domains which associate features of adhesion molecules and proteases. ADAMTSs (a disintegrin and metalloprotease with thrombospondin motifs) bear thrombospondin type I motifs in C-terminal extremity, and most of them are secreted proteins. Because genetic studies have shown that ADAM-33 gene polymorphisms are associated with asthma, we designed this study to assess mRNA expression profile of several ADAM and ADAMTS proteases in sputum from patients with asthma and to investigate the relationship between expression of these proteases and asthma-associated inflammation and airway obstruction. mRNA expression profile of selected ADAM and ADAMTS proteinases (ADAM-8, -9, -10, -12, -15, -17, and -33; ADAMTS-1, -2, -15, -16, -17, -18, and -19), their physiological inhibitors TIMP-1 and TIMP-3, and RECK, a membrane-anchored MMP activity regulator, was obtained by RT-PCR analysis performed on cells collected by sputum induction from 21 patients with mild to moderate asthma and 17 healthy individuals. mRNA levels of ADAM-8, ADAM-9, ADAM-12, TIMP-1, and TIMP-3 were significantly increased, whereas mRNA levels coding for ADAMTS-1, ADAMTS-15, and RECK were significantly decreased in patients with asthma compared with control patients. ADAM-8 expression was negatively correlated with the forced expiratory volume at the first second (FEV(1)) (r = -0.57, P < 0.01), whereas ADAMTS-1 and RECK expressions were positively correlated to FEV(1) (r = 0.45, P < 0.05, and r = 0.55, P = 0.01, respectively). We conclude that expression of ADAMs and ADAMTSs and their inhibitors is modulated in airways from patients with asthma and that these molecules may play a role in the pathogenesis of asthma.

Emerging drugs for chronic lymphocytic leukaemia

Although the philosophy of management of patients with chronic lymphocytic leukaemia (CLL) has been altered with the advent of fludarabine-based therapies, impact on long-term survival is unclear and a significant proportion of patients will develop resistance to fludarabine. Similar to other haematological malignancies, a potential for 'cure' is likely to be achieved only if 'high-quality' complete remissions (CRs) are achieved. Treatment options for patients who develop resistance to fludarabine continue to be limited, with only a proportion obtaining a response (usually not CRs) with salvage therapies. This review summarises novel therapies that are being evaluated in patients with CLL, specifically those targeting the antiapoptotic Bcl-2 family of proteins and receptors (e.g., CD40, CD80, HLA-DR) involved in mediating survival signals from the microenvironment.

Anti-CD23

CD23, the low-affinity immunoglobulin (Ig)E receptor (FcepsilonRII), is widely distributed on the surface of various human cells. CD23 mediates numerous IgE-related immune responses (including allergen focusing) by enhancing IgE antigen complex presentation, regulating IgE synthesis, influencing cell differentiation and growth of both B- and T-cells, and stimulating production of pro-inflammatory mediators from monocytes/macrophages, eosinophils, and even airway smooth muscle cells. Both membrane and soluble CD23 play an important role in allergic reactions. Cellular contacts and cytokines modulate its expression in a concerted manner as needed for allergic reactions. Expression of CD23 and soluble CD23 has been associated with allergic diseases. Targeting CD23 with monoclonal antibody (MAb) is a promising candidate therapy in allergic diseases. A newly developed agent known as Lumiliximab, which is an anti-CD23 MAb (Lumiliximab), was demonstrated to be a well-tolerated agent in a phase I clinical trial (a placebo-controlled study with allergic asthma). Adverse events were mild, and no relationship was apparent between the dose of Lumilixilab and the frequency, severity, or type of event. Sustained and dose-dependent decreases in mean serum total IgE concentrations were noted. The serum half-life of Lumilixilab increased from 2 to 10 d with increasing doses. Blocking antigen presentation, preventing costimulation signals, and reducing production of pro-inflammatory mediators are some of the potential mechanisms involved for anti-CD23 activity. Although the safety and clinical efficacy of Lumilixilab in allergic asthma and rhinitis require confirmation, the observed data imply that anti-CD23 is a promising candidate therapy option for future treatment of allergic diseases.

Production of biologically active recombinant human soluble CD23 and its effect on PBMCs isolated from hyper-IgE blood

A recombinant form of human soluble CD23 (sCD23), the low affinity receptor for IgE (FcepsilonRII), was produced by PCR cloning the lectin-binding domain sequence into a bacterial expression vector. After renaturation and purification, the sCD23 bound IgE and divalent metal ions, indicating its activity. The recombinant human sCD23 exhibited similar proinflammatory properties as the native protein. Although interleukin-1beta, tumour necrosis factor-alpha, and nuclear factor-kappaB appeared not to be enhanced significantly in unstimulated RPMI 8866 B-lymphoblastoid and U937 promonocytic cell lines with 24 h incubation of recombinant sCD23, they were produced in both healthy and hyper-IgE-derived peripheral blood mononuclear cells, especially tumour necrosis factor-alpha. This study concludes that while recombinant and chimeric sCD23 may be useful in blocking IgE binding to immune cells and decreasing IgE synthesis by B-lymphocytes, the production of proinflammatory cytokines, particularly tumour necrosis factor-alpha will enhance immune responses in cases of asthma, allergy, and hyper-IgE syndrome.

Immunosenescence and macrophage functional plasticity: dysregulation of macrophage function by age-associated microenvironmental changes

The macrophage lineage displays extreme functional and phenotypic heterogeneity, which appears to be because, in large part, of the ability of macrophages to functionally adapt to changes in their tissue microenvironment. This functional plasticity of macrophages plays a critical role in their ability to respond to tissue damage and/or infection and to contribute to clearance of damaged tissue and invading microorganisms, to recruitment of the adaptive immune system, and to resolution of the wound and of the immune response. Evidence has accumulated that environmental influences, such as stromal function and imbalances in hormones and cytokines, contribute significantly to the dysfunction of the adaptive immune system. The innate immune system also appears to be dysfunctional in aged animals and humans. In this review, the hypothesis is presented and discussed that the observed age-associated 'dysfunction' of macrophages is the result of their functional adaptation to the age-associated changes in tissue environments. The resultant loss of orchestration of the manifold functional capabilities of macrophages would undermine the efficacy of both the innate and adaptive immune systems. The macrophages appear to maintain functional plasticity during this dysregulation, making them a prime target of cytokine therapy that could enhance both innate and adaptive immune systems.

Differential Induction of IL-1β and TNF by CD40 Ligand or Cellular Contact with Stimulated T Cells Depends on the Maturation Stage of Human Monocytes

Cellular contact with stimulated T cells potently induces cytokine production in monocytes, a mechanism that is likely to be relevant to chronic inflammation. Although the identity of surface molecules involved in this process remains elusive, CD40 and its ligand, CD40L, are thought to be implicated, considering that they are expressed at the inflammatory site. To ascertain the involvement of CD40L, we compared the activation of three different types of human monocytic cells, i.e., freshly isolated monocytes, monocytes primed with IFN-gamma (IFN-gamma-macrophages), and THP-1 cells. These cells were activated by either membranes isolated from stimulated T cells (HUT-78 or T lymphocytes) to mimic cellular contact, soluble extracts from isolated membranes, or CD40L trimer (CD40LT). The production of TNF and IL-1beta was induced by membranes of stimulated T cells in the three types of target cells, whereas CD40LT induced TNF production in IFN-gamma-macrophages only. Similar results were obtained with soluble extracts of T cell membranes, demonstrating that the difference between membranes and CD40LT was not due to the particulate form of membranes. CD40LT induced neither transcript nor protein of cytokines in monocytes, whereas in IFN-gamma-macrophages, IL-1beta and TNF mRNA were observed, but only TNF was measured in cell supernatants. Finally, anti-CD40L Abs failed to inhibit TNF and IL-1beta production induced in IFN-gamma-macrophages by solubilized membranes, whereas TNF production induced by CD40LT was inhibited. These results demonstrate that CD40L is not required in monocyte activation by direct cellular contact with stimulated T cells, although soluble CD40LT induces the production of TNF in IFN-gamma-macrophages.

Expression and regulation of a disintegrin and metalloproteinase (ADAM) 8 in experimental asthma

Asthma, a complex chronic inflammatory pulmonary disorder, is on the rise despite intense ongoing research. To elucidate novel pathways involved in asthma pathogenesis, we used transcript expression profiling in a murine model of asthma. Employing asthma models induced by different allergens (ovalbumin and Aspergillus fumigatus) we uncovered the involvement of ADAM8, a member of a disintegrin and metalloproteinase (ADAM) family. In situ hybridization of mouse lungs revealed strong ADAM8 induction in peribronchial and perivascular inflammatory cells as well as in bronchiolar epithelial cells following allergen challenge. Sequence analysis of lung ADAM8 cDNA identified a novel splice variant of ADAM8 that contained an additional exon in juxtaposition to the transmembrane domain. Allergen-induced ADAM8 mRNA accumulation in the lung was dose- and time-dependent. Transgenic or pharmacologic delivery of interleukin (IL)-4 or IL-13 to the lungs resulted in a marked increase of ADAM8 expression. Gene-targeted mice studies revealed that ovalbumin-induced ADAM8 was largely dependent upon signal transducer and activator of transcription (STAT) 6 and the IL-4 receptor alpha-chain. Thus, ADAM8 is an allergen-, IL-4-, and IL-13-induced gene in the experimental asthmatic lung. Taken together with the role of ADAM33 in asthma, these results suggest that allergic lung responses involve the interplay of diverse members of the ADAM family.

Variations in the serum levels of soluble CD23, nitric oxide and IgE across the spectrum of American cutaneous leishmaniasis

Serum IgE levels and the expression of low affinity receptor for IgE (Fc epsilon RII/CD23) are increased in cutaneous leishmaniasis. The ligation of CD23 receptor by IgE-anti-IgE immune complexes results in nitric oxide (NO) production, which is a critical leishmanicidal factor. Human monocytes/macrophages express Fc epsilon RII/CD23 after activation with IFN-gamma and IL-4. In the present study, we assessed the relationship between NO, total and Leishmania-specific IgE and soluble CD23 across the clinical spectrum of American cutaneous leishmaniasis (ACL). Sixty-nine ACL patients and 22 endemic controls were studied. NO concentration was estimated using the Greiss method. Soluble CD23, total IgE and anti-Leishmania IgE levels were measured using ELISA. Soluble CD23 was increased in the four patient groups (0.001<P<0.05) compared by the Mann-Whitney test to healthy subjects, particularly in mucocutaneous leishmaniasis (MCL) and diffuse cutaneous leishmaniasis (DCL) patients. Total IgE levels were higher in ACL patients (P<0.0001). Anti-Leishmania IgE showed a similar tendency, where MCL and DCL patients had greater levels. All patients groups, except intermediate or chronic cutaneous leishmaniasis (ICL) patients, showed elevated levels of NO(2)(-)/NO(3)(-) compared to healthy individuals (0.001<P<0.01). Interestingly, ICL patients did not produce significant levels of NO(2)(-)/NO(3)(-). ACL patients showed a significant positive correlation between soluble CD23 and anti-Leishmania IgE. DCL patients showed a positive correlation between both parameters. Overall results suggest that sCD23, IgE and NO may play different roles across the ACL spectrum.

Interleukin-1beta, interleukin-6, tumour necrosis factor-alpha and interferon-gamma released by a viral infection and an aseptic inflammation reduce CYP1A1, 1A2 and 3A6 expression in rabbit hepatocytes

Inflammation reduces activity and expression of hepatic cytochrome P450 (P450) and therefore diminishes drug biotransformation. This study aimed to identify the serum mediators triggered by a viral infection and an aseptic inflammation that downregulate P450 isoforms. Incubation of hepatocytes with serum from rabbits with a turpentine-induced inflammation or humans with a viral infection decreased the amount of cytochrome 1A1 (CYP1A1), 1A2 and 3A6 mRNA and apoproteins. By serum fractionation and immuno-neutralization, we showed that in the aseptic inflammation, interleukin-6 and, to a lesser degree, interleukin-1beta are involved in the downregulation of all three isoforms. In serum from humans with a viral infection, interleukin-1beta, interleukin-6, interferon-gamma and tumour necrosis factor-alpha contribute to the downregulation of P450 isoforms. CYP1A1 and 1A2 are regulated by serum mediators at the transcriptional level, while the expression of CYP3A6 appears to be under the control of pre- and posttranscriptional mechanisms.

CD23 shedding: requirements for substrate recognition and inhibition by dipeptide hydroxamic acids

CD23 (low affinity IgE receptor, FcepsilonRII) is expressed as a Type II extracellular protein on a variety of cells such as B cells, monocytes and macrophages and is cleaved from the cell surface to generate several distinct fragments. The expression of CD23 on the cell surface as well as the generation of soluble fragments of CD23 has been shown to be involved in regulation of IgE synthesis. CD23 is released from the cell surface by a metalloprotease, analogous to the cleavage of other cell surface molecules such as TNF-alpha. This activity has been extensively studied with respect to biochemical characterization and ability to cleave specific mutants of CD23. Both local sequence and distal domains have been shown to affect cleavage of CD23. Selective dipeptide hydroxamic acid inhibitors of CD23 processing have been identified and demonstrated to very potently and selectively inhibit CD23 processing.

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.

Expression and purification of stable 33-kDa soluble human CD23 using the Drosophila S2 expression system

CD23, a 45-kDa type II membrane glycoprotein present on B cells, monocytes, and other human immune cells, is a low-affinity receptor for IgE. The extracellular region of the membrane-bound human CD23 is processed into at least four soluble (s) CD23 forms, with apparent molecular masses of 37, 33, 29, and 25 kDa. High levels of sCD23 are found in patients with allergy, certain autoimmune diseases, or chronic lymphocytic leukemia. Therefore, inhibition of the processing of membrane-bound CD23 to control the cytokine-like effects of sCD23 offers a novel therapeutic opportunity. While the 37-, 29-, and 25-kDa forms of sCD23 have been expressed previously as recombinant proteins, the 33-kDa form has not been purified and characterized. To further investigate the multiple roles of sCD23 fragments and to devise assays to identify potent small-molecule inhibitors of CD23 processing, we have produced the 33-kDa form of sCD23 using Chinese hamster ovary (CHO) and Drosophila S2 cells. The CHO-expressed 33-kDa protein was found to undergo proteolytic degradation during cell growth and during storage of purified protein, resulting in accumulation of a 25-kDa form. The Drosophila system expressed the 33-kDa sCD23 in a stable form that was purified and demonstrated to be more active than the CHO-derived 25-kDa form in a monocyte TNFalpha release assay.

Ligation of CD11b and CD11c beta(2) integrins by antibodies or soluble CD23 induces macrophage inflammatory protein 1alpha (MIP-1alpha) and MIP-1beta production in primary human monocytes through a pathway dependent on nuclear factor-kappaB

Chemokines and adhesion molecules such as integrins play a major part in the trafficking, extravasation, and recruitment of leukocytes to inflammatory sites. This study investigated the effects of beta(2) integrin engagement on chemokine production by freshly isolated human monocytes. We found that ligation of CD11b or CD11c but not CD11a alpha chains of beta(2) integrins by antibodies or soluble CD23 (sCD23) fusion proteins rapidly induced transcription and secretion of interleukin 8, macrophage inflammatory protein (MIP) 1alpha, and MIP-1beta. Because the promoters of these chemokine genes contain kappaB binding sites, we assessed the possible role of nuclear factor-kappaB (NF-kappaB) in controlling induction of the genes through beta(2) integrin engagement. Electrophoretic mobility shift assays showed that sCD23 or antibodies to CD11b or to CD11c up-regulated DNA-binding activity of NF-kappaB. Activation of NF-kappaB was accompanied by degradation of its cytosolic inhibitor IkappaB-alpha. Blockade of depletion of IkappaB-alpha by proteasome inhibitors (proteasome inhibitor I or acetyl-leucinyl-leucinyl-norleucinal) led to concomitant inhibition of NF-kappaB DNA-binding activity and expression of MIP-1alpha and MIP-1beta messenger RNA induced by beta(2) integrin ligation. These results suggest that triggering of CD11b or CD11c beta(2) integrin on primary human monocytes provides activation signals leading to nuclear translocation of NF-kappaB and subsequent secretion of MIP-1alpha and MIP-1beta that may have an important role in recruitment of other inflammatory cells during initiation of an inflammatory response.

Engagement of CD11b and CD11c β2 integrin by antibodies or soluble CD23 induces IL-1β production on primary human monocytes through mitogen-activated protein kinase–dependent pathways

β2 integrins are involved in the recruitment of leukocytes to inflammatory sites and in cellular activation. We demonstrate that ligation of CD11b (Mac-1, CR3) or CD11c (p150, CR4) alpha chains of β2 integrins by mAbs or soluble chimeric CD23 (sCD23) on human freshly isolated monocytes rapidly stimulates high levels of interleukin-1β production. This induction takes place at the transcriptional level and is regulated by members of the mitogen-activated protein kinase (MAPK) family. Indeed, stimulation of monocytes through engagement of CD11b or CD11c results in the phosphorylation and activation of ERK1, ERK2, and p38/SAPK2 MAP kinases. U0126, a potent inhibitor of the upstream activator of ERK1/2, ie, MEK1/2, suppresses IL-1β messenger RNA (mRNA) expression in a dose-dependent fashion, showing the implication of this pathway in the transcriptional control of IL-1β production. On the other hand, inhibition of p38 by SB203580 indicates that this MAPK is involved in the control of IL-1β production at both transcriptional and translational levels. Together these data demonstrate that ligation of CD11b and CD11c β2 integrins by mAbs or sCD23 fusion proteins triggers the activation of 2 distinct MAPK signaling pathways that cooperate in controlling IL-1β synthesis at different levels.

Engagement of CD11b and CD11c β2 integrin by antibodies or soluble CD23 induces IL-1β production on primary human monocytes through mitogen-activated protein kinase–dependent pathways

β2 integrins are involved in the recruitment of leukocytes to inflammatory sites and in cellular activation. We demonstrate that ligation of CD11b (Mac-1, CR3) or CD11c (p150, CR4) alpha chains of β2 integrins by mAbs or soluble chimeric CD23 (sCD23) on human freshly isolated monocytes rapidly stimulates high levels of interleukin-1β production. This induction takes place at the transcriptional level and is regulated by members of the mitogen-activated protein kinase (MAPK) family. Indeed, stimulation of monocytes through engagement of CD11b or CD11c results in the phosphorylation and activation of ERK1, ERK2, and p38/SAPK2 MAP kinases. U0126, a potent inhibitor of the upstream activator of ERK1/2, ie, MEK1/2, suppresses IL-1β messenger RNA (mRNA) expression in a dose-dependent fashion, showing the implication of this pathway in the transcriptional control of IL-1β production. On the other hand, inhibition of p38 by SB203580 indicates that this MAPK is involved in the control of IL-1β production at both transcriptional and translational levels. Together these data demonstrate that ligation of CD11b and CD11c β2 integrins by mAbs or sCD23 fusion proteins triggers the activation of 2 distinct MAPK signaling pathways that cooperate in controlling IL-1β synthesis at different levels.

Increased synovial fluid levels of soluble CD23 are associated with an erosive status in rheumatoid arthritis (RA)

Synovial fluid (SF) levels of soluble CD23 (sCD23) were determined in 96 patients presenting with an inflammatory knee effusion (73 with RA and 23 with reactive arthritis (ReA) serving as a control inflammatory non-erosive group) and were correlated with the degree of joint destruction, with local immune parameters (IL-1beta, IL-3, IL-4, IL-6, IL-8, IL-10, IL-12 and sCD25) and with serum markers of inflammation, C-reactive protein and erythrocyte sedimentation rate. RA patients, classified as erosive or not according to Larsen's grade, were separated as follows: (i) 13 patients with non-erosive RA; (ii) 16 RA patients with erosions in hands but not in knees, matched for disease duration with the first group; (iii) 44 RA patients with hand and knee erosions, matched with the second group for rheumatoid factor positivity but of longer disease duration. SF sCD23 levels were significantly increased in both erosive RA groups compared with non-erosive diseases, whether RA or ReA (P < 0.05), whose SF levels were not different. SF IL-10 showed a similar profile to that of SF sCD23 and was the only other parameter characteristic of erosive RA, but no direct correlation was found between the two. SF sCD23 was significantly correlated with IL-12 (r = 0.65, P = 0.0001) and sCD25 (r = 0.39, P = 0.0019) exclusively in the two erosive RA populations. In conclusion, these data showing that increased levels of sCD23 are not only found in the SF of erosive joints but also in knee SF of patients with erosive RA but without knee x-ray-diagnosed erosions suggest that this parameter might be of predictive value for joint destruction. Longitudinal studies are however needed to confirm its potential clinical interest.

In vitro IgE inhibition in B cells by anti-CD23 monoclonal antibodies is functionally dependent on the immunoglobulin Fc domain

CD23, the low affinity receptor for IgE (FcvarepsilonRII), is involved in regulation of IgE synthesis by B-lymphocytes. Five monoclonal antibodies to human CD23 were generated from cynomolgus macaques immunized with purified soluble CD23 (sCD23). Four of the five primate antibodies blocked the binding of IgE complexes to CD23 positive cells and also inhibited the production of IgE in vitro by IL-4 induced human peripheral blood mononuclear cells (PBMC). The variable domains of several primate antibodies were utilized to construct chimeric macaque/human (PRIMATIZED((R))) monoclonal antibodies. PRIMATIZED((R)) p5E8G1, containing human gamma 1 constant region, inhibited IgE production in vitro as efficiently as the parent primate antibody, but the human gamma 4 constant version, PRIMATIZED((R)) p5E8G4, was not as effective in IgE inhibition. An F(ab')(2) of p5E8G1 did not inhibit IgE production but did interfere with IgE inhibition by the intact anti-CD23 antibody in a dose dependent fashion. The murine monoclonal antibody MHM6 recognizes human CD23 at a different epitope than primate antibody 5E8, and inhibits IgE production by IL-4 induced PBMC. As with the F(ab')(2) of p5E8G1, the F(ab')(2) of MHM6 also failed to inhibit IgE production. These data imply that the mechanism by which anti-CD23 antibodies inhibit IgE production requires cross-linking of CD23 to an IgG receptor. These data also imply that neither bivalent cross-linking of CD23 alone or inhibition of CD23 binding to its natural ligands is sufficient to inhibit IgE production.

Characterization of novel FcepsilonRII/CD23 isoforms lacking the transmembrane (TM) segment in human cell lines

Human FcepsilonRII/CD23 is an approximately 45 kDa type II transmembrane glycoprotein belonging to the C-type animal-lectin family, and has two isoforms (a and b) that only differ in their intracytoplasmic tails. We previously found that in several human and mouse cell lines there were two additional CD23 transcripts (a' and b') lacking the exon 3 that encodes the entire transmembrane segment and a part of cytoplasmic tails. In this study, we analyzed the putative CD23a' and CD23b' products at protein levels and characterized with rabbit polyclonal antibodies against novel amino-acid sequences of the putative CD23a' and CD23b' molecules (anti-CD23a' Ab, anti-CD23b' Ab). Western blots in COS cells transfected with CD23a' or CD23b' cDNA as well as in vitro translation assays showed that the a' and b' CD23 transcripts were translated to about 40 kDa molecules. These 40 kDa molecules were also recognized by a polyclonal antibody against 25 kDa soluble fragment of human CD23. We also found that human cells having mRNAs for CD23a' and CD23b' expressed protein products recognized specifically by anti-CD23a' or anti-CD23b' Ab, respectively. In addition, the CD23a' and CD23b' molecules in transfected COS cells were resistant to Endo H(f) and PNGase F, although these truncated forms as well as the membrane-associated forms had an asparagine residue responsible for the N-linked glycosylation. Taken together, our results show that the a' and b' CD23 transcripts are expressed and translated in human lymphoid cells and that their translated products are retained in the cytoplasm where they might play an unique regulatory role in the expression of the full-length CD23 on the cell surface.

CD47 ligation selectively downregulates human interleukin 12 production

Interleukin (IL)-12 plays a key role not only in protective innate and adaptive T helper cell type 1 (Th1) responses but also in chronic inflammatory diseases. We report here that engagement of CD47 by either monoclonal antibody, its natural ligand thrombospondin (TSP), or 4N1K (a peptide of the COOH-terminal domain of TSP selectively binding CD47) inhibits IL-12 release by monocytes. The suppression occurred after T cell-dependent or -independent stimulation of monocytes and was selective for IL-12 inasmuch as the production of tumor necrosis factor (TNF)-alpha, IL-1, IL-6, and granulocyte/macrophage colony-stimulating factor was not inhibited. CD47 ligation did not alter transforming growth factor (TGF)-beta and IL-10 production, and the suppressive effect on IL-12 was not due to autocrine secretion of TGF-beta or IL-10. The IL-12 inhibition was not mediated by Fcgamma receptor ligation, did not require extracellular Ca(2+) influx, but was reversed by two phosphoinositide 3-kinase inhibitors (wortmannin and Ly294002). Thus, engagement of CD47 on monocytes by TSP, which transiently accumulates at the inflammatory site, is a novel and unexplored pathway to selectively downregulate IL-12 response. The pathway may be relevant in limiting the duration and intensity of the inflammatory response, and in developing novel therapeutic strategies for Th1-mediated diseases.

IL-12-Independent costimulation pathways for interferon-gamma production in familial disseminated Mycobacterium avium complex infection

We have described previously a family with an apparent genetic susceptibility to disseminated Mycobacterium avium complex infection and an underlying defect in IL-12 regulation leading to abnormally low interferon-gamma production. Their T cells appear to act normally when in the presence of normal accessory cells. Cell-to-cell contact was necessary for normal monocytes to complement the familial patient monocyte defect, suggesting the familial defect in interferon-gamma costimulation involves pathways requiring cell surface molecule interactions. In an effort to better characterize the abnormality in these patients, we examined the role of known costimulatory molecules in residual costimulation by patient PBMC compared to normals. Whereas normals utilized CD40/CD40L interactions and IL-12 production for optimal interferon-gamma costimulation in PHA-stimulated cocultures, familial patient interferon-gamma production was low and unaffected by their blockade. CD86 blockade caused a greater than 50% reduction in both normal and familial patient interferon-gamma production, implying that a majority of residual familial patient costimulation required this pathway. Furthermore, selected myelomonocytic cell lines (K562 and THP1) acted as potent accessory cells for interferon-gamma production by familial patient and normal T cells, largely independent of IL-12 production. However, CD86 blockade of K562 cell/familial cell cocultures resulted in less than a 20% reduction in interferon-gamma production, indicating that familial patient cells respond to IL-12- and CD86-independent costimulatory signals for interferon-gamma as well. Thus, we demonstrate that the familial defect also involves interferon-gamma costimulation pathways requiring both CD40/CD40L interaction and IL-12 production, while residual pathways remain that allow low-level interferon-gamma production. Familial Mycobacterium avium patient monocytes and certain myelomonocytic cell lines can be exploited to investigate IL-12-independent costimulation for interferon-gamma production.

Lymphocyte Activation Gene-3, a MHC Class II Ligand Expressed on Activated T Cells, Stimulates TNF-α and IL-12 Production by Monocytes and Dendritic Cells

Lymphocyte activation gene-3 (LAG-3) is an MHC class II ligand structurally and genetically related to CD4. Although its expression is restricted to activated T cells and NK cells, the functions of LAG-3 remain to be elucidated. Here, we report on the expression and function of LAG-3 on proinflammatory bystander T cells that are activated in the absence of TCR engagement. LAG-3 is expressed at high levels on human T cells cocultured with autologous monocytes and IL-2 and synergizes with the low levels of CD40 ligand (CD40L) expressed on these cells to trigger TNF-α and IL-12 production by monocytes. Indeed, anti-LAG-3 mAb inhibits both IL-12 and IFN-γ production in IL-2-stimulated cocultures of T cells and autologous monocytes. Soluble LAG-3Ig fusion protein markedly enhances IL-12 production by monocytes stimulated with infra-optimal concentrations of sCD40L, whereas it directly stimulates monocyte-derived dendritic cells (DC) for the production of TNF-α and IL-12, unravelling an enhanced responsiveness to MHC class II engagemenent in DC as compared with activated monocytes. Thus similar to CD40L, LAG-3 may be involved in the proinflammatory activity of cytokine-activated bystander T cells and most importantly it may directly activate DC.

Intractable pruritus in HIV infection: immunologic characterization

BACKGROUND

Severe, intractable pruritus, often associated with erythematopapular skin lesions and hypereosinophilia, is a condition observed in some nonatopic, HIV-infected patients. We performed immunovirologic analyses of this condition.

METHODS

Immunologic (mitogen-stimulated production of cytokines, tumor necrosis factor-alpha [TNF-alpha], and soluble CD23; serum levels of soluble CD23, ICAM-1, TNF-alpha, IgG, IgE, and IgA) and virologic (HIV viral load) parameters were analyzed in six patients with therapy-resistant pruritus. Hypereosinophilia was present in all these patients. Results were compared to those of seven HIV-seropositive individuals similar to the first one in terms of CD4 counts and clinical staging, but without pruritus.

RESULTS

Hypereosinophilia; hyper-IgE and hyper-IgA; augmented interleukin (IL)-4, IL-5, and sCD23; and reduced interferon-gamma production by mitogen-stimulated peripheral blood mononuclear cells (PBMC) were detected when patients with pruritus were compared to HIV controls. HIV viral load was also augmented in patients in whom pruritus was present.

CONCLUSIONS

The results suggest that therapy-resistant, intractable pruritus accompanied by hypereosinophilia may be used to define a subset of HIV-seropositive individuals showing prototypic hyperactivation of humoral immunity, and in whom augmented HIV viral load is present.

The vitronectin receptor and its associated CD47 molecule mediates proinflammatory cytokine synthesis in human monocytes by interaction with soluble CD23

The vitronectin receptor, alphavbeta3 integrin, plays an important role in tumor cell invasion, angiogenesis, and phagocytosis of apoptotic cells. CD47, a member of the multispan transmembrane receptor family, physically and functionally associates with vitronectin receptor (VnR). Although vitronectin (Vn) is not a ligand of CD47, anti-CD47 and beta3 mAbs suppress Vn, but not fibronectin (Fn) binding and function. Here, we show that anti-CD47, anti-beta3 mAb and Vn, but not Fn, inhibit sCD23-mediated proinflammatory function (TNF-alpha, IL-12, and IFN-gamma release). Surprisingly, anti-CD47 and beta3 mAbs do not block sCD23 binding to alphav+beta3+ T cell lines, whereas Vn and an alphav mAb (clone AMF7) do inhibit sCD23 binding, suggesting the VnR complex may be a functional receptor for sCD23. sCD23 directly binds alphav+beta3+/CD47(-) cell lines, but coexpression of CD47 increases binding. Moreover, sCD23 binds purified alphav protein and a single human alphav chain CHO transfectant. We conclude that the VnR and its associated CD47 molecule may function as a novel receptor for sCD23 to mediate its proinflammatory activity and, as such, may be involved in the inflammatory process of the immune response.

Biphasic regulation of the development of murine type II collagen-induced arthritis by interleukin-12: possible involvement of endogenous interleukin-10 and tumor necrosis factor alpha

OBJECTIVE

To examine the dose-specific effects of interleukin-12 (IL-12) on the evolution of murine type II collagen-induced arthritis (CIA).

METHODS

From day 24 through day 33 following primary immunization, mice received daily intraperitoneal injections of murine recombinant IL-12. Measurements of anticollagen IgG, cytokines, and corticosterone were performed using enzyme-linked immunosorbent assay and radioimmunoassay.

RESULTS

CIA mice injected with a low dose of IL-12 (5 ng/day) exhibited accelerated onset and increased severity of arthritis. In contrast, administration of a high dose of IL-12 (500 ng/day) attenuated arthritic inflammation. The low dose of IL-12 induced tumor necrosis factor alpha (TNFalpha) production, whereas the high dose induced production of both IL-10 and corticosterone and suppression of anticollagen antibody levels. Administration of neutralizing anti-TNFalpha and anti-IL-10 antibodies reversed the dose-specific effects of IL-12.

CONCLUSION

IL-12 is an important immunomodulator during the pathogenesis of CIA. It appears to act by regulating humoral and cellular immune responses, as well as by mediating the expression of immunoregulatory cytokines and glucocorticoids.

Inhibitors of the p38 Mitogen-Activated Kinase Modulate IL-4 Induction of Low Affinity IgE Receptor (CD23) in Human Monocytes

CD23, the low affinity IgE receptor, is up-regulated on the surface of IL-4-treated B cells and monocytes and is immediately proteolytically processed, releasing soluble fragments of CD23. Here, we report that inhibitors of the p38 mitogen-activated kinase (p38 MAPK), SK&F 86002 or the more selective inhibitor, SB 203580, reduce the levels of soluble CD23 formed by IL-4-stimulated human monocytes or the human monocytic cell line, U937. In contrast to compounds such as the metalloprotease inhibitor batimastat ([4-(N-hydroxyamino)-2-(R)-isobutyl-3-(S)-(2-thiophenethiomethyl)succinyl]-(S)-phenylalanine-N-methylamide, sodium salt), p38 MAPK inhibitors do not directly inhibit proteolytic processing of CD23. Further, evaluation of surface intact CD23 (iCD23) by flow cytometry demonstrated that SK&F 86002 and SB 203580 reduced the surface expression of iCD23 in a concentration-dependent fashion, while batimastat increased the surface expression of iCD23. The decrease in surface iCD23 was accompanied by a decrease in total cell-associated CD23 protein levels but not CD23 mRNA. IL-4 induced a late (&gt;4-h) increase in p38 MAPK activity and corresponding activation of its substrate MAPKAPK-2. This activation was blocked by addition of SB 203580 before IL-4 induction, in parallel with the inhibition of CD23 expression. Modulation of CD23 by antibodies has been shown to alleviate the symptoms of murine collagen-induced arthritis, implicating CD23 as an important proinflammatory agent. These data show that in addition to the known cytokine inhibitory actions of SK&F 86002 and SB 203580, they also confer an additional potential anti-inflammatory activity through modulation of CD23 expression.

IL-15 Promotes IL-12 Production by Human Monocytes Via T Cell-Dependent Contact and May Contribute to IL-12-Mediated IFN-γ Secretion by CD4+ T Cells in the Absence of TCR Ligation

At inflammatory sites, the number of activated bystander T cells exceeds that of Ag-activated T cells. We investigated whether IL-15, a monocyte-derived cytokine that shares several biologic activities with IL-2, may contribute to bystander T cell activation in the absence of IL-2 and triggering Ag. The addition of IL-15 to cocultures of monocytes and T cells stimulates CD4+ but not CD8+ T cells to produce IFN-γ. IFN-γ production requires endogenous IL-12, the production of which in turn is dependent upon CD40/CD154 interactions between CD4+ T cells and monocytes. Indeed, non-TCR-activated CD4+ but not CD8+ T cells express significant levels of CD154. IL-15 may enhance IFN-γ in this system by up-regulating CD40 expression on monocytes and IL-12Rβ1 expression on CD4+ T cells. Conversely, using neutralizing anti-IL-15 mAb, we show that the ability of IL-12 to augment IFN-γ secretion is partly mediated by endogenous IL-15. Finally, in the absence of monocytes, a synergistic effect between exogenous IL-12 and IL-15 is necessary to induce IFN-γ production by purified CD4+ T cells, while IL-15 alone induces T cell proliferation. It is proposed that this codependence between IL-12 and IL-15 for the activation of inflammatory T cells may be involved in chronic inflammatory disorders that are dominated by a Th1 response. In such a response, a self-perpetuating cycle of inflammation is set forth, because IL-15-stimulated CD4+ T cells may activate monocytes to release IL-12 that synergizes with IL-15 to induce IL-12 response and IFN-γ production.

IFN-α Priming of Human Monocytes Differentially Regulates Gram-Positive and Gram-Negative Bacteria-Induced IL-10 Release and Selectively Enhances IL-12p70, CD80, and MHC Class I Expression

Administration of IFN-γ and IFN-α may protect or induce autoimmune diseases. Although the in vitro regulation of monokine secretion by IFN-γ have been extensively studied, the regulatory function of IFN-α has not yet been elucidated. We compared IFN-α and IFN-γ, added alone or simultaneously before bacterial stimulation, for the control of monokine release and the expression of costimulatory molecules by human monocytes. Our data show that: 1) IFN-α primes monocytes for increased production of IL-10 in response to Staphylococcus aureus Cowan I strain (SAC) but not to LPS, leading to a lack of IFN-α priming for TNF-α secretion; 2) pretreatment of monocytes with IFN-α inhibits LPS- or SAC-induced IL-12p40 production but unexpectedly enhances the release of the biologically active form of IL-12 (IL-12p70); 3) IFN-α and IFN-γ exert an antagonistic effect on LPS- and SAC-induced IL-10 as well as IL-12p40 release, whereas they further enhance IL-12p70 production when added simultaneously; 4) in contrast to IFN-α, IFN-γ primes monocytes to enhance LPS- or SAC-induced TNF-α and IL-12 production, but surprisingly, it increases IL-10 production by monocytes following LPS but not SAC stimulation; and finally, 5) IFN-α pretreatment selectively up-regulates CD80 and MHC class I expression on monocytes. It is proposed that the outcome of the immune response at the site of inflammation may depend on both the type of bacterial injury (Gram-positive or -negative) and of locally produced IFNs, and that the differential and opposite effects of type I and type II IFNs on monocytes may account for the beneficial or detrimental effects of IFN-α therapy.

Anti-adenovirus immune responses in rats are enhanced by interleukin 4 but not interleukin 10 produced by recombinant adenovirus

Recombinant adenoviruses can be used for in vivo gene transfer with great efficiency. However, the duration of transgene expression and the possibility of readministering the virus are severely limited by the host anti-adenovirus immune response, which is controlled mainly by cytokine networks. Adenoviruses encoding IL-4 (AdIL-4) or IL-10 (AdIL-10) were administered to rats through the portal vein and the anti-adenovirus immune response was studied. As compared with administering adenoviruses without transgene (Addl324) or with the lacZ gene (AdlacZ), AdIL-4, but not AdIL-10, resulted in a significant increase in leukocytes in the liver, with a predominance of macrophages that peaked on days 7 and 14 after gene transfer and gradually returned to normal by day 28. AdIL-4 induced a significant increase in both neutralizing and ELISA-detected anti-adenovirus antibodies, whereas AdIL-10 caused an increase in ELISA-detected antibodies alone. Anti-adenovirus antibodies were predominantly of Th1-dependent immunoglobulin subclasses in rats receiving Addl324, AdlacZ, or AdIL-10, whereas animals receiving AdIL-4 showed a predominance of Th2-dependent immunoglobulin subclasses. Type 1 (IFN-gamma) and type 2 (IL-5) cytokines were increased only in livers from rats receiving AdIL-4. Rats receiving AdIL-4 showed increased anti-adenovirus cytotoxic T lymphocyte activity and CD8+ cell depletion prevented leukocyte infiltration in the liver. These results show that IL-4 increases local and systemic immune responses against recombinant adenoviruses.

CD23/Fc epsilon RII: signaling and clinical implication

CD23 is an activation antigen expressed by various human hematopoietic cells, tissular epithelial cells and represents the major low affinity receptor for IgE (Fc epsilon RII). In its membrane and soluble forms, CD23 has multiple ligands that enable this molecule to trigger various functions in human and murine cells. In this issue, we discussed the intracellular signaling events induced by soluble CD23 and the ligand involved in each target cell. Signal transduction through surface CD23 ligation is linked to cyclic nucleotides and nitric oxide (NO) pathways in various human cells and in rat macrophages. Recent in vivo data suggest a regulatory role for these signals during various human physiopathological situations such as hemopoiesis, anti-tumoral defense, inflammation, allergy, microbicidal activity of macrophages and eosinophils, skin disease, and HIV infection.

Immunoglobulin-E/dinitrophenyl complexes induce nitric oxide synthesis in rat peritoneal macrophages by a mechanism involving CD23 and NF-kappa B activation

The production of nitric oxide (NO) by rat adherent peritoneal cells stimulated with preformed IgE/Dinitrophenyl-BSA (DNP-BSA) complexes and its dependence on the activation of the transcription factor NF-kappa B were studied. Stimulation with IgE/DNP-BSA complexes at equivalence induced both the production of NO and an increased expression of the inducible isoform of NO synthase (iNOS) protein. Both events were also elicited by a rabbit polyclonal F(ab')2 anti-CD23 cross-reacting with rat CD23, thus suggesting Fc epsilon RII/CD23 antigen as the IgE-binding structure involved in the triggering of the response and ruling out an interaction of the antibody via its Fc portion. Inhibition of redox-sensitive signaling mechanisms by the antioxidant pyrrolidine dithiocarbamate (PDTC) blocked NO production, iNOS expression, and NF-kappa B activation elicited by both IgE/DNP-BSA complexes and anti-CD23 F(ab')2, thus suggesting the involvement of NF-kappa B in the signaling pathway leading to the transcriptional activation of iNOS. These results show the existence in rat peritoneal macrophages of a signaling pathway triggered by CD23 engagement that promotes nuclear translocation of NF-kappa B and transcriptional activation of the inducible isoform of NO synthase.

Anti-FcepsilonRIalpha autoantibodies in autoimmune-mediated disorders. Identification of a structure-function relationship

Anti-FcepsilonRIalpha autoantibodies (autoAbs) occur and may be of pathogenetic relevance in a subset of chronic urticaria (CU) patients. To analyze the prevalence and magnitude of the humoral anti-FcepsilonRIalpha response in cohorts of CU patients compared with individuals suffering from classic skin- related (auto)immune diseases, we developed an ELISA system for the measurement of anti-FcepsilonRIalpha autoAbs in nonfractionated serum samples. Results obtained using this assay correlated well with those generated by Western blotting. We found IgG anti-FcepsilonRIalpha autoreactivity in 38% of CU patients but not in atopic dermatitis patients, psoriatics, or healthy individuals. We frequently detected anti-FcepsilonRIalpha autoAbs in pemphigus vulgaris (PV, 39%), dermatomyositis (DM, 36%), systemic lupus erythematosus (SLE, 20%), and bullous pemphigoid (BP, 13%). While the autoAb titers in DM, SLE, BP, and PV were similar to those encountered in CU patients, only anti-FcepsilonRIalpha+ CU serum specimens displayed pronounced histamine-releasing activity. The anti-FcepsilonRIalpha autoAbs in CU patients belong predominantly to the complement-fixing subtypes IgG1 and IgG3, whereas in DM, PV, and BP, they were found to be mainly of the IgG2 or IgG4 subtype. Complement-activating properties of anti-FcepsilonRIalpha autoAbs can indeed be of pathogenetic relevance, because C5a receptor blockade on basophils as well as decomplementation reduced drastically the histamine-releasing capacity of most anti-FcepsilonRIalpha-reactive CU sera. As a consequence, therapeutic efforts in CU should aim at altering not only the quantity but also the complement-activating properties of IgG anti-FcepsilonRIalpha autoAbs.

Regulation of human cytotoxic T lymphocytes development by the synergistic effect of IL-7 and sCD23

The present study was undertaken to investigate the interaction of IL-7 and sCD23 on human peripheral blood T cell activation and CTL differentiation. Purified T lymphocytes were stimulated with mitogen plus IL-2 and subcultured for 7 days with IL-7 and/or sCD23. The combination of IL-7 and sCD23 synergistically enhanced the proliferation of both CD4+ and CD8+. T cells. CD8+ T cells, however, were usually more responsive to IL-7 and sCD23. This synergy was observed on both subsets of T cells. Furthermore, these cytokines synergistically augment the CTL activity of CD8+ T cells in both mitogen- and antigen-activated T cells. MAbs anti-IL-2 or anti-IL-2R (CD25) and anti-IL-12 had no effect on T cell proliferation and CD8+ cytotoxic activity induced by IL-7 and sCD23. We analyzed the effect on IFN-gamma induction by CD8+ T cells and found that IL-7 alone was incapable of inducing detectable levels of IFN-gamma production, but together with sCD23 it enhanced the production of IFN-gamma. We also found that IFN-gamma was not required for enhanced CTL activity of CD8+ T cells, because rabbit anti-IFN-gamma did not block the synergistic effects of either cytokine. The data demonstrate that the synergistic stimulatory activity of IL-7 and sCD23 may be of significance in the human CTL development and provide an alternative mechanism of stimulating T cells for use in immunotherapy.

IgE secretion is attenuated by an inhibitor of proteolytic processing of CD23 (Fc epsilonRII)

CD23, the low-affinity IgE receptor, is up-regulated on interleukin (IL)-4-stimulated B cells and monocytes, with a concomitant increase in the release of soluble fragments of CD23 (sCD23) into the medium by proteolytic processing of the surface-bound intact CD23. The effect of inhibition of the processing of CD23 on IgE production in human and mouse cells and in a mouse model in vivo was evaluated. CD23 processing to sCD23 from RPMI 8866 (a human Epstein-Barr virus-transformed B cell line) cell membranes was inhibited by a broad-spectrum matrix-metalloprotease inhibitor, batimastat, with an IC50 of 0.15 microM. Batimastat also inhibited CD23 processing in whole RPMI 8866 cells as well as in IL-4-stimulated purified human monocytes with similar IC50. Batimastat inhibited IgE production from IL-4/anti-CD40-stimulated human tonsil B cells as well as mouse splenic B cells in a manner consistent with inhibition of CD23 processing. Release of soluble fragments of CD23 in the cell supernatants of tonsil B cells was inhibited over the concentration range of 1-10 microM batimastat and intact cell surface CD23 was increased on mouse splenic B cells in the presence of these concentrations of batimastat. IgE production of IL-4-stimulated human peripheral blood mononuclear cells was also blocked by 1-10 microM batimastat, again with comparable inhibition of sCD23 release over the same concentration range. Finally, in a mouse model of IgE production, batimastat inhibited IgE production in response to ovalbumin challenge as determined by serum IgE levels. Taken together, the data support a role of CD23 in IgE production and point to CD23 processing to sCD23 as a therapeutically relevant control point in the regulation of IgE synthesis.

Characterization of a constitutive type III nitric oxide synthase in human U937 monocytic cells: stimulation by soluble CD23

The soluble cleavage fragment of the low-affinity immunoglobulin E (IgE) receptor/CD23 (sCD23 25000 MW) and antibodies directed against their receptors on monocytes, CD11b and CD11c, stimulate the production of nitric oxide (NO) by these cells and we have suggested that the enzyme involved could be related to the endothelial constitutive type III nitric oxide synthase (ecNOS). In the present work, we have analysed the characteristic properties of this NOS isoform in the model of the human promonocytic cells U937 By reverse-transcription polymerase chain reaction (RT-PCR), the presence of an mRNA coding for type III NOS was found in U937 cells and the corresponding protein was detected by immunofluorescence in permeabilized cells with a specific anti-ecNOS monoclonal antibody (mAb). Membrane extracts displayed a NOS activity dependent on the presence of calcium and calmodulin in the reaction medium and that was abrogated in the presence of EGTA. Recombinant soluble CD23 (25000 MW) was found to trigger an NO-dependent cGMP accumulation in these cells, which was abrogated by calcium chelators and inhibitors of the calcium/calmodulin complex. Moreover, sCD23 elicited a transient augmentation of intracytoplasmic free calcium concentration [Ca2+]i that was dependent on the presence of calcium in the external buffer and was prevented in the presence of EGTA, indicating that it was due to a calcium influx. In conclusion, human promonocytic cells such as U937 exhibit a functional type III NOS that can be stimulated by calcium-raising agents, such as sCD23.

IL-10 suppresses cell surface CD23/Fc epsilon RII expression, not by enhancing soluble CD23 release, but by reducing CD23 mRNA expression in human monocytes

To examine a possible involvement of interleukin-10 (IL-10) in CD23/Fc epsilon RII expression in human monocytes, effects of IL-10 on the cell surface CD23 expression, soluble CD23 (sCD23) release, and CD23 type b mRNA expression were investigated. IL-10 suppressed IL-4-induced surface CD23 expression on monocytes in a dose-dependent manner, and this effect was completely neutralized by anti-IL-10 antibody. The suppressive effect of IL-10 on surface CD23 expression was not due to enhancement of sCD23 release from the cell surface because no increase in sCD23 in culture supernatant was detected after incubation with IL-10. Instead, the effect of IL-10 seemed to be exerted at the transcriptional level since IL-4-induced expression of CD23 type b mRNA was significantly reduced when IL-10 was present. Although IL-4 induced surface CD23 expression on both monocytes and B cells, the suppressive effect of IL-10 was observed only on monocytes, which underscores different regulatory mechanisms for CD23 expression between the two cell types.

Functional CD40 ligand expression on T lymphocytes in the absence of T cell receptor engagement: involvement in interleukin-2-induced interleukin-12 and interferon-gamma production

Despite the fact that the great majority of T cells at the site of an inflammatory response are not antigen specific, the mechanisms leading to activation and recruitment of these bystander T cells are poorly understood. We previously reported that soluble (s)CD23 potentiated the interleukin (IL)-2-induced interferon (IFN)-gamma production by T cells co-cultured with autologous monocytes in the absence of T cell receptor (TCR) engagement. Our present data demonstrate that the IL-2-induced IFN-gamma secretion, in the presence but also in the absence of sCD23, is strictly IL-12 dependent, inasmuch as anti-IL-12 antibody abrogated both responses. Most interestingly, anti-CD40 ligand (CD40L) monoclonal antibody significantly inhibited IL-2-induced IL-12 as well as IFN-gamma production. These results suggest that CD40L was expressed on T cells in the absence of TCR engagement. Indeed, purified unstimulated T cells readily expressed CD40L. IL-2 and monocytes did not up-regulate CD40L on resting T cells. It is proposed that low levels of CD40L expression on non-antigen stimulated T cells are sufficient to signal through CD40 molecules on accessory cells and to induce IL-12 secretion, which in turn can synergize with IL-2 for the induction of IFN-gamma production, thus contributing to the inflammatory process.

Regulation of the balance of cytokine production and the signal transducer and activator of transcription (STAT) transcription factor activity by cytokines and inflammatory synovial fluids

The balance between type 1 and 2 T helper cell cytokine production plays an important role in several animal models of autoimmunity, and skewed patterns of cytokine expression have been described in human inflammatory diseases. Many cytokines activate signal transducer and activation of transcription (STAT) transcription factors, which, in turn, activate transcription of inflammatory effector genes. We used mononuclear cell priming cultures and inflammatory synovial fluids (SFs) derived from arthritis patients to examine the regulation of cytokine production and STAT activity by an inflammatory synovial microenvironment. Exposure to SFs during priming resulted in an 81% inhibition of interferon (IFN)-gamma, but not interleukin (IL) 4, production by effector cells generated in priming cultures. SF suppression was mediated by IL-4 and IL-10 and inhibition of IL-12 expression, and it was reversed in a dominant fashion by exogenous IL-12. SFs blocked the sustained activity of transcription factor Stat1, but not Stat3, during the priming period, and Stat1 activity was differentially regulated by cytokines in parallel with their positive or negative regulation of IFN-gamma production. Active Stat3, but not Stat1, was detected in cells from inflamed joints. These results suggest a role for altered balance of Stat1 and Stat3 transcriptional activity in the regulation of T cell differentiation and in the pathogenesis of inflammatory synovitis.