Pleiotropic role of lyn kinase in leukotriene B4–induced eosinophil activation

Eosinophils and Purinergic Signaling in Health and Disease

Eosinophils are major effector cells against parasites, fungi, bacteria, and viruses. However, these cells also take part in local and systemic inflammation, which are central to eczema, atopy, rhinitis, asthma, and autoimmune diseases. A role for eosinophils has been also shown in vascular thrombotic disorders and in cancer. Many, if not all, above-mentioned conditions involve the release of intracellular nucleotides (ATP, ADP, UTP, etc.) and nucleosides (adenosine) in the extracellular environment. Simultaneously, eosinophils further release ATP, which in autocrine and paracrine manners, stimulates P2 receptors. Purinergic signaling in eosinophils mediates a variety of responses including CD11b induction, ROI production, release of granule contents and enzymes, as well as cytokines. Exposure to extracellular ATP also modulates the expression of endothelial adhesion molecules, thereby favoring eosinophil extravasation and accumulation. In addition, eosinophils express the immunosuppressive adenosine P1 receptors, which regulate degranulation and migration. However, pro-inflammatory responses induced by extracellular ATP predominate. Due to their important role in innate immunity and tissue damage, pharmacological targeting of nucleotide- and nucleoside-mediated signaling in eosinophils could represent a novel approach to alleviate eosinophilic acute and chronic inflammatory diseases. These innovative approaches might also have salutary effects, particularly in host defense against parasites and in cancer.

Characterization of the APETALA2/Ethylene-responsive factor (AP2/ERF) transcription factor family in sunflower

One of the most prominent families of genes in plants is the AP2/ERF which play an important role in regulating plant growth and responses to various stresses. In this research, a genome-wide survey was conducted to recognize the AP2/ERF genes in sunflower (Helianthus annuus L.), and a total of 288 HaAP2/ERF was obtained. Phylogenetic analysis divided them into four sub-families, including 248 ERF, 4 RAV and 35 AP2, and one subgroup of the Soloist family. Localization of chromosome, gene structure, the conserved motif, gene ontology, interaction networks, homology modeling, the modeling of cis-regulatory elements and the analysis of events in the duplication of genes were carried out for HaAP2/ERF genes. Finally, 9AP2/ERF genes were chosen to confirm the gene expression of the selected genes in leaf and root tissues in various abiotic stress conditions by qPCR. The results confirmed that AP2/ERFs genes could effectively resist abiotic stress. Also, proline content was studied under drought, salinity, cold and heat stress. The results indicated that proline was increased under abiotic stress. This research has been done for the first time to determine the HaAP2/ERF family, which prepared valuable data for the evolutionary and practical research regarding AP2/ERF in sunflower.

Role of leukotrienes in diabetic retinopathy

The pathophysiology of diabetic retinopathy is highly complex and encompasses the detrimental roles of numerous factors/mediators in inducing various molecular pathological alterations. Although the roles of many inflammatory mediators, involved in the progression of this complication, have been thoroughly researched and studied, the part played by leukotrienes remains widely neglected. This review focuses on leukotrienes-induced mediation and aggravation of the pathological pathways, such as inflammation, oxidative stress and retinal angiogenesis, responsible for exhibition of various characteristic events including leukostasis, macular edema, retinal neovascularization and vitreous hemorrhages, hence, marking the advent of diabetic retinopathy. Acknowledging these roles, it might be possible to potentially utilize leukotrienes antagonists for suppressing or reducing the intensity of the mentioned pathological alterations. Hence, leukotrienes antagonists may act as an effective adjuvant therapy either along with other developing novel therapies (such as anti-VEGF or anti-TNF-α therapy), or with the established conventional laser photocoagulation treatment, to provide additional symptomatic relief or, possibly prevent the progression of diabetic retinopathy.

Genome-Wide Analysis of the AP2/ERF Transcription Factors Family and the Expression Patterns of DREB Genes in Moso Bamboo (Phyllostachys edulis)

The AP2/ERF transcription factor family, one of the largest families unique to plants, performs a significant role in terms of regulation of growth and development, and responses to biotic and abiotic stresses. Moso bamboo (Phyllostachys edulis) is a fast-growing non-timber forest species with the highest ecological, economic and social values of all bamboos in Asia. The draft genome of moso bamboo and the available genomes of other plants provide great opportunities to research global information on the AP2/ERF family in moso bamboo. In total, 116 AP2/ERF transcription factors were identified in moso bamboo. The phylogeny analyses indicated that the 116 AP2/ERF genes could be divided into three subfamilies: AP2, RAV and ERF; and the ERF subfamily genes were divided into 11 groups. The gene structures, exons/introns and conserved motifs of the PeAP2/ERF genes were analyzed. Analysis of the evolutionary patterns and divergence showed the PeAP2/ERF genes underwent a large-scale event around 15 million years ago (MYA) and the division time of AP2/ERF family genes between rice and moso bamboo was 15–23 MYA. We surveyed the putative promoter regions of the PeDREBs and showed that largely stress-related cis-elements existed in these genes. Further analysis of expression patterns of PeDREBs revealed that the most were strongly induced by drought, low-temperature and/or high salinity stresses in roots and, in contrast, most PeDREB genes had negative functions in leaves under the same respective stresses. In this study there were two main interesting points: there were fewer members of the PeDREB subfamily in moso bamboo than in other plants and there were differences in DREB gene expression profiles between leaves and roots triggered in response to abiotic stress. The information produced from this study may be valuable in overcoming challenges in cultivating moso bamboo.

Bafetinib inhibits functional responses of human eosinophils in vitro

Eosinophils play a prominent role in the process of allergic inflammation. Non-receptor associated Lyn tyrosine kinases generate key initial signals in eosinophils. Bafetinib, a specific Abl/Lyn tyrosine kinase inhibitor has shown a potent antiproliferative activity in leukemic cells, but its effects on eosinophils have not been reported. Therefore, we studied the effects of bafetinib on functional and mechanistic responses of isolated human eosinophils. Bafetinib was more potent than non-specific tyrosin kinase comparators genistein and tyrphostin inhibiting superoxide anion triggered by N-formyl-Met-Leu-Phe (fMLF; 100 nM) (-log IC50=7.25 ± 0.04 M; 6.1 ± 0.04 M; and 6.55 ± 0.03 M, respectively). Bafetinib, genistein and tyrphostin did not modify the [Ca(2+)]i responses to fMLF. Bafetinib inhibited the release of EPO induced by fMLF with higher potency than genistein and tyrphostin (-log IC50=7.24 ± 0.09 M; 5.36 ± 0.28 M; and 5.37 ± 0.19 M, respectively), and nearly suppressed LTC4, ECP and chemotaxis. Bafetinib, genistein and tyrphostin did not change constitutive apoptosis. However bafetinib inhibited the ability of granulocyte-monocyte colony-stimulating factor to prevent apoptosis. The activation of Lyn tyrosine kinase, p-ERK1/2 and p-38 induced by fMLF was suppressed by bafetinib and attenuated by genistein and tyrphostin. In conclusion, bafetinib inhibits oxidative burst and generation of inflammatory mediators, and reverses the eosinophil survival. Therefore, future anti-allergic therapies based on bafetinib, could help to suppress excessive inflammatory response of eosinophils at inflammatory sites.

Regulation of endothelial connexin40 expression by shear stress

Endothelial connexin (Cx)40 plays an important role in signal propagation along blood vessel walls, modulating vessel diameter and thereby blood flow. Blood flow, in turn, has been shown to alter endothelial Cx40 expression. However, the timing and shear stress dependence of this relationship have remained unclear, as have the signal transduction pathways involved and the functional implications. Therefore, the aim of this study was to quantify the effects of shear stress on endothelial Cx40 expression, to analyze the role of phosphoinositide 3-kinase (PI3K)/Akt signaling involved, and to assess the possible functional consequences for the adaptation of microvascular networks. First-passage human umbilical vein endothelial cells were exposed to defined shear stress conditions and analyzed for Cx40 using real-time RT-PCR and immunoblot analysis. Shear stress caused long-term induction of Cx40 protein expression, with two short-term mRNA peaks at 4 and 16 h, indicating the dynamic nature of the adaptation process. Maximum shear stress-dependent induction was observed at shear levels between 6 and 10 dyn/cm(2). Simulation of this pattern of shear-dependent Cx expression in a vascular adaptation model of a microvascular network led to an improved fit for the simulated results to experimental measurements. Cx40 expression was greatly reduced by inhibiting PI3K or Akt, with PI3K activity being required for basal Cx40 expression and Akt activity taking part in its shear stress-dependent induction.

The signaling mechanism of eosinophil activation

Eosinophils play an important role in certain aspects of asthma pathogenesis. This review focuses on the mechanism of activation of eosinophils by the growth factor interleukin-5 and the CC chemokine receptor-3. Interleukin-5 activates members of the Janus and Src family of kinases. The latter kinases are largely responsible for the generation of initial signaling events. CC chemokine receptor-3, in contrast, signals through heterotrimeric G-proteins. Subsequently, various signaling pathways are activated, which converge on four major pathways - the mitogen-activated protein kinase pathway, the phosphoinositide-3 kinase pathway, the calcium signaling pathway and the Janus-signal transducer and activator of transcription signaling pathway. The biologic consequences of many of these signaling pathways are also discussed.

Dual acylation and lipid raft association of Src-family protein tyrosine kinases are required for SDF-1/CXCL12-mediated chemotaxis in the Jurkat human T cell lymphoma cell line

Chemokines play pivotal roles in regulating a wide variety of biological processes by modulating cell migration and recruitment. Deregulation of chemokine signaling can alter cell recruitment, contributing to the pathogenic states associated with autoimmune disease, inflammatory disorders, and sepsis. During chemotaxis, lipid rafts and their resident signaling molecules have been demonstrated to partition to different parts of the cell. Herein, we investigated the role of lipid raft resident Src-family kinases (SFK) in stromal cell-derived factor 1/CXCL12-mediated chemotaxis. We have shown that Lck-deficient J.CaM 1.6 cells are defective in CXCL12-mediated chemotaxis in contrast to their parental counterpart, Jurkat cells. Ectopic expression of the SFK hematopoietic cell kinase (Hck) in J.CaM 1.6 cells reconstituted CXCL12 responsiveness. The requirement of lipid raft association of SFK was assessed using both isoforms of Hck: the dually acylated p59(Hck) isoform that is targeted to lipid rafts and the monoacylated p61(Hck) isoform that is nonraft-associated. We have shown using several gain and loss of acylation alleles that dual acylation of Hck was required for CXCL12-mediated chemotaxis in J.CaM 1.6 cells. These results highlight the importance of the unique microenvironment provided by lipid rafts and their specific contribution in providing specificity to CXCL12 signaling.

CD66b regulates adhesion and activation of human eosinophils

Eosinophils and their products are likely important in the pathophysiology of allergic diseases, such as bronchial asthma, and in host immunity to parasitic organisms. However, the mechanisms for proinflammatory mediator release by eosinophils are poorly understood. CD66b (CEACAM8, CGM6, NCA-95) is a single chain, GPI-anchored, highly glycosylated protein belonging to the carcinoembryonic Ag supergene family. CD66b is an activation marker for human granulocytes; however, its biological functions are largely unknown in eosinophils. We found that CD66b is highly expressed on the surface of human peripheral blood eosinophils isolated from healthy individuals. Engagement of CD66b, but not CD66a, by mAb or a natural ligand, galectin-3, activated a Src kinase family molecule, hemopoietic cell kinase (Hck), and induced cellular adhesion, superoxide production, and degranulation of eosinophils. CD66b molecules were localized in lipid rafts, and disruption of lipid rafts or removal of the GPI anchor inhibited the adhesion and activation of eosinophils. Importantly, CD66b was constitutively and physically associated with a beta2 integrin, CD11b, and cross-linking of CD66b induced a striking clustering of CD11b molecules. Thus, CD66b molecules are involved in regulating adhesion and activation of eosinophils, possibly through their localization in lipid rafts and interaction with other cell surface molecules, such as CD11b. Binding of exogenous or endogenous carbohydrate ligands(s) to CD66b may be important in the release of proinflammatory mediators by human eosinophils.

A dual activation and inhibition role for the paired immunoglobulin-like receptor B in eosinophils

The accumulation of eosinophils in inflammatory foci is a hallmark characteristic of Th2 inflammation. Nevertheless, the expression of inhibitory receptors such as paired immunoglobulin-like receptor B (PIR-B) and their function regulating eosinophil accumulation have received limited attention. We now report that Pirb was up-regulated in an eosinophil-dependent manner in the lungs of allergen-challenged and interleukin (IL)-13-overexpressing mice. Eosinophils expressed high levels of PIR-B, and Pirb(-/-) mice displayed increased gastrointestinal eosinophils. Consistent with these findings, PIR-B negatively regulated eotaxin-dependent eosinophil chemotaxis in vivo and in vitro. Surprisingly, Pirb(-/-) eosinophils and neutrophils had decreased leukotriene B4 (LTB(4))-dependent chemotactic responses in vitro. Furthermore, eosinophil accumulation was decreased in a chitin-induced model, partially dependent on LTB(4). Mechanistic analysis using a miniphosphoproteomic approach revealed that PIR-B recruits activating kinases after LTB(4) but not eotaxin stimulation. Consequently, eotaxin-activated Pirb(-/-) eosinophils displayed markedly increased extracellular signal-related kinase 1 and 2 (ERK1/2) phosphorylation, whereas LTB(4)-activated eosinophils had reduced ERK1/2 phosphorylation. We provide multiple lines of evidence supporting a model in which PIR-B displays opposing but potent regulatory functions in granulocyte activation. These data change the conventional wisdom that inhibitory receptors are restricted to inhibitory signals; we therefore propose that a single receptor can have dual functionality in distinct cell types after unique cellular signals.

Using guinea pigs in studies relevant to asthma and COPD

The guinea pig has been the most commonly used small animal species in preclinical studies related to asthma and COPD. The primary advantages of the guinea pig are the similar potencies and efficacies of agonists and antagonists in human and guinea pig airways and the many similarities in physiological processes, especially airway autonomic control and the response to allergen. The primary disadvantages to using guinea pigs are the lack of transgenic methods, limited numbers of guinea pig strains for comparative studies and a prominent axon reflex that is unlikely to be present in human airways. These attributes and various models developed in guinea pigs are discussed.

Biologic therapies for the treatment of asthma

Asthma is a chronic disease of the airway whose pathogenesis involves the complex interplay between many cell types and inflammatory mediators. The mainstays of therapy, inhaled bronchodilators and corticosteroids, do not target the asthmatic airway specifically and therefore are associated with untoward side effects. Anti-IgE (omalizumab) is the only biologic therapy to have transitioned completely from bench to bedside. Other candidate therapies, such as those that alter the T-helper 1/T-helper 2 cytokine balance, interfere with inflammatory cell trafficking, or modify normal intracellular signaling cascades involved in inflammatory gene transcription, have had only limited success in human clinical trials. This article describes several potential novel biologic therapies that have been or could be investigated.

Kinase inhibitors and airway inflammation

Kinases are believed to play a crucial role in the expression and activation of inflammatory mediators in the airway, in T-cell function and airway remodelling. Important kinases such as Inhibitor of kappaB kinase (IKK)2, mitogen activated protein (MAP) kinases and phsopho-inositol (PI)3 kinase regulate inflammation either through activation of pro-inflammatory transcription factors such as activating protein-1 (AP-1) and nuclear factor kappaB (NF-kappaB), which are activated in airway disease, or through regulation of mRNA half-life. Selective kinase inhibitors have been developed which reduce inflammation and some characteristics of disease in animal models. Targeting specific kinases that are overexpressed or over active in disease should allow for selective treatment of respiratory diseases. Interest in this area has intensified due to the success of the specific Abelson murine leukaemia viral oncogene (Abl) kinase inhibitor imatinib mesylate (Gleevec) in the treatment of chronic myelogenous leukaemia. Encouraging data from animal models and primary cells and early Phase I and II studies in other diseases suggest that inhibitors of p38 MAP kinase and IKK2 may prove to be useful novel therapies in the treatment of severe asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis and other inflammatory airway diseases.

Activation of human eosinophils via P2 receptors: novel findings and future perspectives

A growing body of information indicates that release of intracellular nucleotides represents an important way to modulate several cell pathways in physiological or pathological conditions. Nucleotides released as a consequence of cell damage, cell stress, bacterial infection, or other noxious stimuli signal at a class of plasma membrane receptors--P2 receptors--activating diverse intracellular pathways in many tissues and organs. For example, nucleotides secreted in the airway system control chloride/liquid secretion, goblet cell degranulation, and ciliary beat frequency. Several studies indicate that nucleotides play a role in airway diseases through their action on multiple cell types, including mast cells, dendritic cells, neurons, and eosinophils. Recent work by us and other groups led to the identification and characterization of P2 receptors expressed by human eosinophils. In this review, we will summarize recent developments in this field and put forward a hypothesis about the role of P2 receptors in pathophysiological conditions where eosinophils are major players.

Novel signal transduction modulators for the treatment of airway diseases

Multiple signal transduction pathways are involved in the inflammatory process in the airways of patients with asthma and chronic obstructive pulmonary disease (COPD), hence modulators of these pathways may result in novel anti-inflammatory treatments. The advantage of this approach is that these pathways are activated in many inflammatory and structural cells of the airways, hence a broad spectrum of anti-inflammatory effects may be possible. However, this also makes it more likely that side effects may be limiting, but this may not be a problem if the signal transduction pathway is selectively activated in disease and the therapeutic index may be increased by inhaled delivery. Phosphodiesterase-4 (PDE4) inhibitors are the most advanced treatment in this category as anti-inflammatory treatment for asthma and COPD, although side effects are dose limiting. Other promising approaches are inhibitors of p38 mitogen-activated protein (MAP) kinase, inhibitor of nuclear factor-kappaB kinase-2 (IKK2), and Syk kinase, all of which are in clinical development. Several other kinases and transcription factors are also targets for novel drug development. It is likely that modulators of signal transduction pathways may lead to the development of several novel anti-inflammatory treatments for asthma and COPD in the future.

Involvement of BLT1 Endocytosis and Yes Kinase Activation in Leukotriene B4-Induced Neutrophil Degranulation

One of the important biological activities of human neutrophils is degranulation, which can be induced by leukotriene B4 (LTB4). Here we investigated the intracellular signaling events involved in neutrophil degranulation mediated by the high affinity LTB4 receptor, BLT1. Peripheral blood neutrophils as well as the promyeloid PLB-985 cell line, stably transfected with BLT1 cDNA and differentiated into a neutrophil-like cell phenotype, were used throughout this study. LTB4-induced enzyme release was inhibited by 50-80% when cells were pretreated with the pharmacological inhibitors of endocytosis sucrose, Con A and NH4Cl. In addition, transient transfection with a dominant negative form of dynamin (K44A) resulted in approximately 70% inhibition of ligand-induced degranulation. Pretreating neutrophils or BLT1-expressing PLB-985 cells with the Src family kinase inhibitor PP1 resulted in a 30-60% inhibition in BLT1-mediated degranulation. Yes kinase, but not c-Src, Fgr, Hck, or Lyn, was found to exhibit up-regulated kinase activity after LTB4 stimulation. Moreover, BLT1 endocytosis was found to be necessary for Yes kinase activation in neutrophils. LTB4-induced degranulation was also sensitive to inhibition of PI3K. In contrast, it was not affected by inhibition of the mitogen-activated protein kinase MEK kinase, the Janus kinases, or the receptor tyrosine kinase epidermal growth factor receptor or platelet-derived growth factor receptor. Taken together, our results suggest an essential role for BLT1 endocytosis and Yes kinase activation in LTB4-mediated degranulation of human neutrophils.

New drugs for asthma

Asthma is a major and increasing global health problem and, despite major advances in therapy, many patients' symptoms are not adequately controlled. Treatment with combination inhalers, which contain a corticosteroid and long-acting beta(2) adrenoceptor agonist, is the most effective current therapy. There is therefore a search for new therapies, particularly safe and effective oral treatments and those that are more efficacious in severe asthma. New therapies in development include mediator antagonists and inhibitors of cytokines, although these therapies might be too specific to be very effective. New anti-inflammatory therapies include corticosteroids and inhibitors of phosphodiesterase-4, p38 mitogen-activated protein kinase and nuclear factor-kappaB. The prospects for a curative treatment are on the horizon.

Biochemical assessment of intracellular signal transduction pathways in eosinophils: implications for pharmacotherapy

Allergic asthma and allergic rhinitis are inflammatory diseases of the airway. Cytokines and chemokines produced by T helper (Th) type 2 cells (GM-CSF, IL-4, IL-5, IL-6, IL-9, IL-10 and IL-13), eotaxin, transforming growth factor-beta, and IL-11 orchestrate most pathophysiological processes of the late-phase allergic reaction, including the recruitment, activation, and delayed apoptosis of eosinophils, as well as eosinophilic degranulation to release eosinophilic cationic protein, major basic protein, and eosinophil-derived neurotoxin. These processes are regulated through an extensive network of interactive intracellular signal transduction pathways that have been intensively investigated recently. Our present review updates the cytokine and chemokine-mediated signal transduction mechanisms including the RAS-RAF-mitogen-activated protein kinases, Janus kinases (signal transducers and activators of transcription), phosphatidylinositol 3-kinase, nuclear factor-kappa B, activator protein-1, GATA, and cyclic AMP-dependent pathways, and describes the roles of different signaling pathways in the regulation of eosinophil differentiation, recruitment, degranulation, and expression of adhesion molecules. We shall also discuss different biochemical methods for the assessment of various intracellular signal transduction molecules, and various antagonists of receptors, modulators, and inhibitors of intracellular signaling molecules, many of which are potential therapeutic agents for treating allergic diseases.

Kinase targets and inhibitors for the treatment of airway inflammatory diseases: the next generation of drugs for severe asthma and COPD?

Kinases are believed to play a crucial role in the expression and activation of inflammatory mediators in the airway, in T-cell function, and in airway remodeling. Important pro-inflammatory transcription factors such as activating protein-1 and nuclear factor kappaB, which are activated in airway disease, require kinase activation to switch on inflammatory genes, while other kinases can regulate mRNA half-life. Selective kinase inhibitors have been developed that reduce inflammatory gene expression and some characteristics of disease in animal models. Targeting specific kinases that are overexpressed or overactive in disease should allow for selective treatment of airway inflammatory diseases. Interest in this area has intensified due to the success of the specific Abelson murine leukemia viral oncogene homolog tyrosine kinase inhibitor, imatinib mesylate, in the treatment of chronic myelogenous leukemia. Encouraging data from animal models and primary cells and early phase I and II studies in other diseases suggest that inhibitors of p38 mitogen-activated protein kinase and inhibitor of kappaB kinase-2 may prove to be useful novel therapies in the treatment of severe asthma and chronic obstructive pulmonary disease.

Crosstalk between BCR/ABL oncoprotein and CXCR4 signaling through a Src family kinase in human leukemia cells

Stromal-derived factor (SDF)-1 and its G protein-coupled receptor, CXCR4, regulate stem/progenitor cell migration and retention in the marrow and are required for hematopoiesis. We show here an interaction between CXCR4 and the Src-related kinase, Lyn, in normal progenitors. We demonstrate that CXCR4-dependent stimulation of Lyn is associated with the activation of phosphatidylinositol 3-kinase (PI3-kinase). This chemokine signaling, which involves a Src-related kinase and PI3-kinase, appears to be a target for BCR/ABL, a fusion oncoprotein expressed only in leukemia cells. We show that the binding of phosphorylated BCR/ABL to Lyn results in the constitutive activation of Lyn and PI3-kinase, along with a total loss of responsiveness of these kinases to SDF-1 stimulation. Inhibition of BCR/ABL tyrosine kinase with STI571 restores Lyn responsiveness to SDF-1 signaling. Thus, BCR/ABL perturbs Lyn function through a tyrosine kinase-dependent mechanism. Accordingly, the blockade of Lyn tyrosine kinase inhibits both BCR/ABL-dependent and CXCR4-dependent cell movements. Our results demonstrate, for the first time, that Lyn-mediated pathological crosstalk exists between BCR/ABL and the CXCR4 pathway in leukemia cells, which disrupts chemokine signaling and chemotaxis, and increases the ability of immature cells to escape from the marrow. These results define a Src tyrosine kinases-dependent mechanism whereby BCR/ABL (and potentially other oncoproteins) dysregulates G protein-coupled receptor signaling and function of mammalian precursors.

Lck is required for stromal cell-derived factor 1 alpha (CXCL12)-induced lymphoid cell chemotaxis

Stromal cell-derived factor 1alpha (CXCL12) induces chemotaxis of lymphocytes through its receptor CXCR4. We examined the role of nonreceptor tyrosine kinases in CXCL12-induced chemotaxis of T cells and natural killer (NK) cells. Damnacanthal, a specific Lck inhibitor, but not the Syk inhibitor piceatannol, inhibited CXCL12-induced chemotaxis of both lymphocyte subsets. Similarly, damnacanthal was shown to inhibit CXCL12-induced chemotaxis of the Jurkat T-cell line. Stimulating T and NK cells with CXCL12 increased both the tyrosine phosphorylation and the kinase activity of Lck. A direct involvement of Lck in CXCL12-induced chemotaxis was demonstrated in the Lck-deficient Jurkat-derived cell line JCaM1.6. Although JCaM1.6 cells express CXCR4, no significant migration was detected after CXCL12 stimulation. Reconstitution with wild-type Lck restored both CXCL12-induced chemotaxis and Lck activation. Furthermore, cotransfection of wild-type Lck with C-terminal Src kinase (Csk) into JCaM1.6 failed to restore the chemotactic response induced by CXCL12. Finally, by targeting critical residues in the Src homology-2 (SH2) or SH3 domains of Lck, we observed that the SH3 domain is important for the function of Lck in CXCL12-mediated chemotaxis. Together, these results suggest a role for Lck in CXCL12-induced signaling pathways leading to lymphocyte chemotaxis.

Fgr deficiency results in defective eosinophil recruitment to the lung during allergic airway inflammation

Using a mouse model of allergic lung inflammation, we found that mice deficient of Fgr, a Src family tyrosine kinase highly expressed in myelomonocytic cells, fail to develop lung eosinophilia in response to repeated challenge with aerosolized OVA. Both tissue and airway eosinophilia were markedly reduced in fgr(-/-) mice, whereas mice with the sole deficiency of Hck, another Src family member, responded normally. Release of allergic mediators, such as histamine, IL-4, RANTES/CCL5, and eotaxin/CCL11, in the airways of OVA-treated animals was equal in wild-type and fgr(-/-) mice. However, lung eosinophilia in Fgr-deficient mice correlated with a defective accumulation of GM-CSF and IL-5 in the airways, whereas secretion of these cytokines by spleen cells in response to OVA was normal. Examination of mRNA expression in whole lung tissue allowed us to detect comparable expression of transcripts for eotaxin/CCL11, macrophage-inflammatory protein-1 alpha/CCL3, macrophage-inflammatory protein-1 beta/CCL4, monocyte chemoattractant protein-1/CCL2, TCA-3/CCL1, IL-4, IL-10, IL-2, IL-3, IL-9, IL-15, and IFN-gamma in OVA-sensitized wild-type and fgr(-/-) mice. In contrast, the increase in IL-5 and IL-13 mRNA expression was lower in fgr(-/-) compared with wild-type mice. These findings suggest that deficiency of Fgr results in a marked reduction of lung eosinophilia and the establishment of a positive feedback loop based on autocrine secretion of eosinophil-active cytokines. These results identify Fgr as a novel pharmacological target to control allergic inflammation.

Lyn tyrosine kinase is important for IL-5-stimulated eosinophil differentiation

IL-5 plays a pivotal role in growth and differentiation of eosinophils. The signal transduction mechanism of IL-5Ralpha is largely unknown. We have demonstrated that IL-5 induces tyrosine phosphorylation of IL-5Ralpha in eosinophils. To identify IL-5Ralpha-associated tyrosine kinases, we have examined the expression of Src family tyrosine kinases in eosinophils. Among the Src family members, Lyn, Hck, Fgr, and Lck are present in eosinophils, and, among these four kinases, only Lyn is associated with the IL-5Ralpha under basal conditions. We also confirm the association of Janus kinase (Jak)2 with IL-5Ralpha. Lyn kinase phosphorylates both IL-5Ralpha and betacR in vitro. The importance of Lyn kinase for eosinophil differentiation was studied using antisense oligodeoxynucleotides. Lyn antisense oligodeoxynucleotide blocks eosinophil differentiation from stem cells in a dose-dependent manner. The Jak2 inhibitor tyrphostin AG490 also inhibits eosinophil differentiation. The importance of Lyn for eosinophil differentiation was further studied using Lyn knockout mice. The IL-5-stimulated eosinophil differentiation from bone marrow cells is significantly inhibited in Lyn(-/-) mice as compared with that in control mice. We conclude that both Lyn and Jak2 play an essential role in IL-5Ralpha signaling, leading to eosinophil differentiation. The effect of Lyn appears to be relatively specific for the eosinophilic lineage.

Eosinophils, allergy and parasites

Recently, known eosinophil functions have been extended considerably: previously the cells were thought to have an exclusive role in the release of cytotoxic mediators; now they are known to have roles in antigen presentation and immunoregulation through the release of cytokines. Although questionable, animal models indicate a rather beneficial role of eosinophils in parasitic infections but a detrimental one, together with other cells, in allergy.

Pharmacological comparison of LTB(4)-induced NADPH oxidase activation in adherent and non-adherent guinea-pig eosinophils

1. Leukotriene B(4) (LTB(4)) stimulation of guinea-pig peritoneal eosinophils, induced a biphasic activation of the NADPH oxidase composed of a rapid (<3 min) phase mediated by non-adherent cells and a sustained (3 - 120 min) phase mediated by CD11b/CD18 adherent eosinophils. Studies were undertaken to compare the intracellular mechanism that mediate these responses. 2. SB 203580 and PP1, inhibitors of p38 mitogen-activated protein (MAP) kinase and the src-family protein tyrosine kinases, respectively caused concentration-dependent attenuation of both the rapid (SB203580: pD(2)=-6.31; PP1: pD(2)=-5.50) and sustained (SB203580: pD(2)=-6.50; PP1: pD(2)=-5.73) phases. Similarly, the MAP kinase kinase-1 inhibitor, PD098059 produced partial inhibition of the both phases of superoxide generation. 3. The protein kinase C (PKC) inhibitors Ro-31 8220, GF 109203X and Gö 6976 attenuated the rapid NADPH oxidase response (pD(2)s=-6.10, -6.72, -6.15 respectively) and, to a lesser extent, (pD(2)s=-5.54, -6.02, -6.51 respectively) the sustained phase. 4. An inhibitor of phosphatidylinositol 3-kinase (PtdIns 3-kinase), wortmannin caused concentration dependent attenuation of the sustained (pD(2)=-8.68) but not rapid phase of superoxide generation. In contrast, the syk kinase inhibitor, piceatannol abolished the rapid (pD(2)=-6.43) but not sustained respiratory responses. 5. This study demonstrates that LTB(4)-induced superoxide generation from adherent and non-adherent eosinophils is mediated via both common (p38 MAP kinase, MEK-1, PKC and the src kinases) and divergent intracellular pathways (syk kinases and PtdIns 3-kinase). This suggests the possibility of therapeutic intervention to selective attenuate activation of adherent tissue eosinophils.

New directions in allergic diseases: mechanism-based anti-inflammatory therapies

Advances in our understanding of allergic inflammation have led to the development of several novel anti-inflammatory drugs that target specific aspects of the inflammatory process. These treatments are based on improvements in existing therapies or on a better understanding of the cellular and molecular mechanisms involved in atopic diseases. Although most attention has been focused on asthma, treatments that inhibit the atopic disease process would have application to all atopic diseases, which often coincide. Specific agents that are now in development for the treatment of allergic inflammation include inhibitors of eosinophilic inflammation (eg, anti-IL-5, CCR3 antagonists, and very late antigen 4 inhibitors), drugs that may inhibit allergen presentation, and inhibitors of T(H)2 cells. More general anti-inflammatory approaches include novel cortico-steroids, phosphodiesterase inhibitors, and mitogen-activated protein kinase inhibitors. Most of the new therapies in development are aimed at inhibiting or suppressing components of the allergic inflammatory response, but in the future, there are possibilities for development of preventive and curative treatments.