Motoyasu Iikura

IL-33 can promote survival, adhesion and cytokine production in human mast cells

IL-33 is a recently identified member of the IL-1 family of molecules, which also includes IL-1 and IL-18. IL-33 binds to the receptor, T1/ST2/IL-1R4, and can promote cytokine secretion by Th2 cells and NF-κB phosphorylation in mouse mast cells. However, the effects of these molecules, especially IL-33, in human mast cells are poorly understood. Expression of the receptors for IL-1 family molecules, specifically, IL-1R1, IL-18R and T1/ST2, was detectable intracellularly in human umbilical cord blood-derived mast cells (HUCBMCs) by flow cytometry, but was scarcely detectable on the cells’ surface. However, IL-1β, IL-18 or IL-33 induced phosphorylation of Erk, p38 and JNK in naïve HUCBMCs, and IL-33 or IL-1β, but not IL-18, enhanced the survival of naive HUCBMCs and promoted their adhesion to fibronectin. IL-33 or IL-1β also induced IL-8 and IL-13 production in naïve HUCBMCs, and enhanced production of these cytokines in IgE/anti-IgE-stimulated HUCBMCs, without enhancing secretion of either PGD2 or histamine. Moreover, IL-33-mediated IL-8 production by HUCBMCs was markedly reduced by the p38 MAPK inhibitor, SB203580. In contrast to findings with mouse mast cells, IL-18 neither induced nor enhanced secretion of the mediators PGD2 or histamine by HUCBMCs. Our findings identify previously unknown functions of IL-33 in human mast cells. One of these is that IL-33, like IL-1β, can induce cytokine production in human mast cells even in the absence of stimuli of FcɛRI aggregation. Our findings thus support the hypothesis that IL-33 may enhance mast cell function in allergic disorders and other settings, either in the presence or absence of co-stimulation of mast cells via IgE/antigen–FcɛRI signals.

Mast Cells Enhance T Cell Activation: Importance of Mast Cell Costimulatory Molecules and Secreted TNF

We recently reported that mast cells stimulated via FcεRI aggregation can enhance T cell activation by a TNF-dependent mechanism. However, the molecular mechanisms responsible for such IgE-, Ag- (Ag-), and mast cell-dependent enhancement of T cell activation remain unknown. In this study we showed that mouse bone marrow-derived cultured mast cells express various costimulatory molecules, including members of the B7 family (ICOS ligand (ICOSL), PD-L1, and PD-L2) and the TNF/TNFR families (OX40 ligand (OX40L), CD153, Fas, 4-1BB, and glucocorticoid-induced TNFR). ICOSL, PD-L1, PD-L2, and OX40L also are expressed on APCs such as dendritic cells and can modulate T cell function. We found that IgE- and Ag-dependent mast cell enhancement of T cell activation required secreted TNF; that TNF can increase the surface expression of OX40, ICOS, PD-1, and other costimulatory molecules on CD3+ T cells; and that a neutralizing Ab to OX40L, but not neutralizing Abs to ICOSL or PD-L1, significantly reduced IgE/Ag-dependent mast cell-mediated enhancement of T cell activation. These results indicate that the secretion of soluble TNF and direct cell-cell interactions between mast cell OX40L and T cell OX40 contribute to the ability of IgE- and Ag-stimulated mouse mast cells to enhance T cell activation.

IL-33 induces IL-13 production by mouse mast cells independently of IgE-FcεRI signals

The IL‐1‐related molecules, IL‐1 and IL‐18, can promote Th2 cytokine production by IgE/antigen‐FcεRI‐stimulated mouse mast cells. Another IL‐1‐related molecule, IL‐33, was identified recently as a ligand for T1/ST2. Although mouse mast cells constitutively express ST2, the effects of IL‐33 on mast cell function are poorly understood. We found that IL‐33, but not IL‐1β or IL‐18, induced IL‐13 and IL‐6 production by mouse bone marrow‐derived, cultured mast cells (BMCMCs) independently of IgE. In BMCMCs incubated with the potently cytokinergic SPE‐7 IgE without specific antigen, IL‐33, IL‐1β, and IL‐18 each promoted IL‐13 and IL‐6 production, but the effects of IL‐33 were more potent than those of IL‐1β or IL‐18. IL‐33 promoted cytokine production via a MyD88‐dependent but Toll/IL‐1R domain‐containing adaptor‐inducing IFN‐β‐independent pathway. By contrast, IL‐33 neither induced nor enhanced mast cell degranulation. At 200 ng/ml, IL‐33 prolonged mast cell survival in the absence of IgE and impaired survival in the presence of SPE‐7 IgE, whereas at 100 ng/ml, IL‐33 had no effect on mast cell survival in the absence of IgE and reduced mast cell survival in the presence of IgE. These observations suggest potential roles for IL‐33 in mast cell‐ and Th2 cytokine‐associated immune responses and disorders.

An IL-1 Cytokine Member, IL-33, Induces Human Basophil Activation via Its ST2 Receptor

Basophils are thought to play pivotal roles in allergic inflammation through rapid release of chemical mediators in addition to sustained production of Th2 cytokines, including IL-4. A newly identified cytokine, IL-33, has been recognized as one of the key cytokines enhancing Th2-balanced immune regulation through its receptor, ST2. The present study was conducted to elucidate whether IL-33 acts directly on, and affects the functions of, human basophils. Real-time PCR analysis showed that basophils express transcripts for ST2. The expression levels were significantly higher compared with eosinophils and neutrophils, and treatment with IL-33 significantly up-regulated basophil ST2 mRNA expression. Expressions of IL-4 and IL-13 mRNA were also up-regulated by IL-33, and there was also enhanced secretion of IL-4 protein. IL-33 increased the surface levels of basophil CD11b expression and enhanced basophil adhesiveness. Although IL-33 failed to directly induce degranulation or attract basophils, it exerted priming effects on basophils. It enhanced degranulation in response to IgE-crosslinking stimulus and also enhanced basophil migration toward eotaxin without changing surface CCR3. Also, IL-33 synergistically enhanced IL-4 production and CD11b expression by IL-3-stimulated basophils. Neutralization using Ab specific for ST2 significantly diminished the enhancing effects of IL-33 on both basophil CD11b expression and migration toward eotaxin, indicating that IL-33 signals via ST2 expressed on basophils. This study revealed that IL-33 potently regulates migration and activation of human basophils. IL-33 may be a key cytokine in the pathogenesis of Th2-dominant inflammation by acting not only on lymphocytes but also on effector cells such as basophils.

Intracellular localization and release of eotaxin from normal eosinophils

Eotaxin is a potent and selective CC chemokine for eosinophils and basophils. We established several monoclonal antibodies (Mabs) allowing the neutralization and measurement of human eotaxin. Using the Mabs as probes, we demonstrated that normal eosinophils contained intracellular granule‐associated eotaxin. Quantification of cell‐associated eotaxin in different leukocyte subsets revealed that it was principally expressed in eosinophils. Finally, we showed that normal eosinophils released eotaxin upon stimulation with either of two secretagogues, C5a or ionomycin. These findings raise the possibility that eosinophil‐derived eotaxin contributes to the local accumulation of eosinophils at the site of inflammation.

Chemokine receptors in human basophils: inducible expression of functional CXCR4

We examined the expression profile of chemokine receptors in humanbasophils and their regulation by cytokines. Basophils expressedtranscripts of CC chemokine receptors (CCR)1, CCR2, CCR3, and CCR5 andCXC chemokine receptors (CXCR)1, CXCR2, and CXCR4. In contrast to theother receptors, surface‐CXCR4 expression was not detected in fresh‐and whole‐blood basophils, but it became apparent gradually duringincubation. Among 16 chemokines tested, eotaxin induced the most potentbasophil migration. SDF‐1 also induced a strong, migratory responsecomparable with that induced by eotaxin in 24‐h, cultured basophils,but it failed to induce degranulation. IL‐3 abrogated CXCR4 expressioncompletely, and it only down‐regulated CCR2 and CCR3 expressionslightly. IL‐5, GM‐CSF, and IL‐4 also down‐regulated CXCR4 expression.Thus, expression of CXCR4 was the most strongly affected by cytokines,and this may represent an alternative mechanism for control ofcell‐specific, biological responses to SDF‐1.

Increased risk of nontuberculous mycobacterial infection in asthmatic patients using long-term inhaled corticosteroid therapy

Background and objective:  The risk of pneumonia is increased among COPD patients using inhaled corticosteroids (ICS). However, there is uncertainty regarding the association between long‐term use of ICS and exacerbations of respiratory tract infections among asthmatic patients.

Exogenous Nitric Oxide Regulates the Degranulation of Human Basophils and Rat Peritoneal Mast Cells

This study was designed to investigate whether anti-IgE-induced or ionophore A23187-induced histamine release from human basophils is regulated by exogenous nitric oxide (NO), and to assess some similarities between the effect of NO on basophils and that on rat peritoneal mast cells (RPMC). The NO donor, sodium nitroprusside (SNP), inhibited A23187-induced histamine release from crude human basophils and crude RPMC in a dose-dependent fashion. This downregulation was still observed when SNP was washed out just before the cell stimulation, indicating that the effect of SNP was irreversible. The downregulation disappeared in both purified cell populations after the removal of contaminating cells. However, when purified cells were preincubated with SNP in the presence of 5 mM N-acetylcysteine (NAC), increasing the bioavailability of NO, the downregulation was recovered. The presence of NAC significantly augmented the downregulation of SNP on A23187-induced histamine release from both crude cell populations. In contrast, SNP had no effect on anti-IgE-induced histamine release from either crude or purified basophil preparation in the absence of NAC, and SNP plus NAC inhibited anti-IgE-induced histamine release from both cell preparations. The same results were obtained with crude and purified RPMC preparations under the same conditions. These results show that SNP similarly downregulated exocytosis of basophils and RPMC, and acquired the potent effect in the presence of NAC, indicating that exogenous NO plays a part in the regulation of basophil and mast cell activation.

Paracrine IL-33 Stimulation Enhances Lipopolysaccharide-Mediated Macrophage Activation

Background IL-33, a member of the IL-1 family of cytokines, provokes Th2-type inflammation accompanied by accumulation of eosinophils through IL-33R, which consists of ST2 and IL-1RAcP. We previously demonstrated that macrophages produce IL-33 in response to LPS. Some immune responses were shown to differ between ST2-deficient mice and soluble ST2-Fc fusion protein-treated mice. Even in anti-ST2 antibody (Ab)-treated mice, the phenotypes differed between distinct Ab clones, because the characterization of such Abs (i.e., depletion, agonistic or blocking Abs) was unclear in some cases. Methodology/Principal Findings To elucidate the precise role of IL-33, we newly generated neutralizing monoclonal Abs for IL-33. Exogenous IL-33 potentiated LPS-mediated cytokine production by macrophages. That LPS-mediated cytokine production by macrophages was suppressed by inhibition of endogenous IL-33 by the anti-IL-33 neutralizing mAbs. Conclusions/Significance Our findings suggest that LPS-mediated macrophage activation is accelerated by macrophage-derived paracrine IL-33 stimulation.

Transendothelial migration of human basophils

During allergic reactions, basophils migrate from the blood compartment to inflammatory sites, where they act as effector cells in concert with eosinophils. Because transendothelial migration (TEM) represents an essential step for extravasation of cells, for the first time we have studied basophil TEM using HUVEC. Treatment of HUVEC with IL-1β significantly enhanced basophil TEM, which was further potentiated by the presence of a CCR3-specific ligand, eotaxin/CCL11. In addition to CCR3 ligands, MCP-1/CCL2 was also active on basophil TEM. Although stromal cell-derived factor-1/CXCL12, a CXCR4 ligand, failed to induce TEM in freshly isolated basophils, it caused strong TEM in 24-h cultured cells. IL-3 enhanced basophil TEM by increasing the chemokinetic response. Spontaneous TEM across activated HUVEC was inhibited by treatment of cells with anti-CD18 mAb, but not with anti-CD29 mAb, and also by treatment of HUVEC with anti-ICAM-1 mAb. Anti-VCAM-1 mAb alone failed to inhibit TEM, but showed an additive inhibitory effect in combination with anti-ICAM-1 mAb. In contrast, eotaxin- and IL-3-mediated TEM was significantly inhibited by anti-CD29 mAb as well as anti-CD18 mAb. These results indicate that β2 integrins play the primary role in basophil TEM, but β1 integrins are also involved, especially in TEM of cytokine/chemokine-stimulated basophils. In conclusion, the regulatory profile of basophil TEM is very similar to that reported for eosinophils. Our results thus support the previous argument for a close relationship between basophils and eosinophils and suggest that the in vivo kinetics of these two cell types are similar.