Lin Ying Liu

Decreased Expression of Membrane IL-5 Receptor α on Human Eosinophils: I. Loss of Membrane IL-5 Receptor α on Airway Eosinophils and Increased Soluble IL-5 Receptor α in the Airway After Allergen Challenge

IL-5 is a key cytokine for eosinophil maturation, recruitment, activation, and possibly the development of inflammation in asthma. High concentrations of IL-5 are present in the airway after Ag challenge, but the responsiveness of airway eosinophils to IL-5 is not well characterized. The objectives of this study were to establish, following airway Ag challenge: 1) the expression of membrane (m)IL-5Rα on bronchoalveolar lavage (BAL) eosinophils; 2) the responsiveness of these cells to exogenous IL-5; and 3) the presence of soluble (s)IL-5Rα in BAL fluid. To accomplish these goals, blood and BAL eosinophils were obtained from atopic subjects 48 h after segmental bronchoprovocation with Ag. There was a striking reduction in mIL-5Rα on airway eosinophils compared with circulating cells. Furthermore, sIL-5Rα concentrations were elevated in BAL fluid, but steady state levels of sIL-5Rα mRNA were not increased in BAL compared with blood eosinophils. Finally, BAL eosinophils were refractory to IL-5 for ex vivo degranulation, suggesting that the reduction in mIL-5Rα on BAL eosinophils may regulate IL-5-mediated eosinophil functions. Together, the loss of mIL-5Rα, the presence of sIL-5Rα, and the blunted functional response (degranulation) of eosinophils to IL-5 suggest that when eosinophils are recruited to the airway, regulation of their functions becomes IL-5 independent. These observations provide a potential explanation for the inability of anti-IL-5 therapy to suppress airway hyperresponsiveness to inhaled Ag, despite a reduction in eosinophil recruitment.

Decreased Expression of Membrane IL-5 Receptor α on Human Eosinophils: II. IL-5 Down-Modulates Its Receptor Via a Proteinase-Mediated Process

In the accompanying study, we demonstrated that following Ag challenge, membrane (m)IL-5Rα expression is attenuated on bronchoalveolar lavage eosinophils, soluble (s)IL-5Rα is detectable in BAL fluid in the absence of increased steady state levels of sIL-5Rα mRNA, and BAL eosinophils become refractory to IL-5 for ex vivo degranulation. We hypothesized that IL-5 regulates its receptor through proteolytic release of mIL-5Rα, which in turn contributes to the presence of sIL-5Rα. Purified human peripheral blood eosinophils were incubated with IL-5 under various conditions and in the presence of different pharmacological agents. A dose-dependent decrease in mIL-5Rα was accompanied by an increase in sIL-5Rα in the supernatant. IL-5 had no ligand-specific effect on mIL-5Rα or sIL-5Rα mRNA levels. The matrix metalloproteinase-specific inhibitors BB-94 and GM6001 and tissue inhibitor of metalloproteinase-3 partially inhibited IL-5-mediated loss of mIL-5Rα, suggesting that sIL-5Rα may be produced by proteolytic cleavage of mIL-5Rα. IL-5 transiently reduced surface expression of β-chain, but had no effect on the expression of GM-CSFRα. Pretreatment of eosinophils with a dose of IL-5 that down-modulated mIL-5Rα rendered these cells unable to degranulate in response to further IL-5 stimulation, but they were fully responsive to GM-CSF. These findings suggest that IL-5-activated eosinophils may lose mIL-5Rα and release sIL-5Rα in vivo, which may limit IL-5-dependent inflammatory events in diseases such as asthma.

IL-5 and Granulocyte-Macrophage Colony-Stimulating Factor Activate STAT3 and STAT5 and Promote Pim-1 and Cyclin D3 Protein Expression in Human Eosinophils

Allergic inflammation is characterized by elevated eosinophil numbers and by the increased production of the cytokines IL-5 and GM-CSF, which control several eosinophil functions, including the suppression of apoptosis. The JAK/STAT pathway is important for several functions in hemopoietic cells, including the suppression of apoptosis. We report in this study that STAT3, STAT5a, and STAT5b are expressed in human eosinophils and that their signaling pathways are active following IL-5 or GM-CSF treatment. However, in airway eosinophils, the phosphorylation of STAT5 by IL-5 is reduced, an event that may be related to the reduced expression of the IL-5Rα on airway eosinophils. Furthermore, IL-5 and GM-CSF induced the protein expression of cyclin D3 and the kinase Pim-1, both of which are regulated by STAT-dependent processes in some cell systems. Pim-1 is more abundantly expressed in airway eosinophils than in blood eosinophils. Because Pim-1 reportedly has a role in the modulation of apoptosis, these results suggest that Pim-1 action is linked to the suppression of eosinophil apoptosis by these cytokines. Although cyclin D3 is known to be critical for cell cycle progression, eosinophils are terminally differentiated cells that do not proceed through the cell cycle. Thus, this apparent cytokine regulation of cyclin D3 suggests that there is an alternative role(s) for cyclin D3 in eosinophil biology.

Generation of Th1 and Th2 Chemokines by Human Eosinophils: Evidence for a Critical Role of TNF-α

Emerging evidence suggests a role for eosinophils in immune regulation of T cells. Thus, we sought to determine whether human eosinophils may exert their effect via differential generation of Th1 and Th2 chemokines depending on cytokines in their microenvironment and, if so, to establish the conditions under which these chemokines are produced. Eosinophils cultured with TNF-α plus IL-4 had increased mRNA expression and protein secretion of the Th2-type chemokines, CCL17 (thymus and activation-regulated chemokine) and CCL22 (macrophage-derived chemokine). Conversely, the Th1-type chemokines, CXCL9 (monokine induced by IFN-γ) and CXCL10 (IFN-γ-inducible protein-10), were expressed after stimulation with TNF-α plus IFN-γ. Addition of TNF-α appeared to be essential for IFN-γ-induced release of Th1-type chemokines and significantly enhanced IL-4-induced Th2-type chemokines. Inhibition of NF-κB completely blocked the production of both Th1 and Th2 chemokines. Activation of NF-κB, STAT6, and STAT1 was induced in eosinophils by TNF-α, IL-4, and IFN-γ, respectively. However, there was no evidence for enhancement of these signaling events when eosinophils were stimulated with the combination of TNF-α plus IL-4 or TNF-α plus IFN-γ. Thus, independently activated signaling cascades appear to lead to activation of NF-κB, STAT1, and STAT6, which may then cooperate at the promoter level to increase gene transcription. Our data demonstrate that TNF-α is a vital component for eosinophil chemokine generation and that, depending on the cytokines present in their microenvironment, eosinophils can promote either a Th2 or a Th1 immune response, supporting an immunoregulatory role for eosinophils.

Chemokine receptor expression on human eosinophils from peripheral blood and bronchoalveolar lavage fluid after segmental antigen challenge

BACKGROUND The recruitment of circulating eosinophils to the lung is a characteristic feature of allergic airway inflammation. Chemokine receptors likely play a role in this complex process. However, reports of chemokine receptor expression on human eosinophils are conflicting. OBJECTIVE The aim of this study was to determine whether the chemokine receptor profile of human eosinophils change when these cells are recruited to the airway after an antigen challenge and development of an allergic inflammatory response. METHODS Blood and bronchoalveolar lavage (BAL) cells were obtained from 13 allergic subjects 48 hours after segmental bronchoprovocation with antigen. The CC chemokine receptor (CCR) 1 to 7, 9, and CXC chemokine receptor (CXCR) 1 to 4 were determined by flow cytometric analysis of whole blood and unseparated BAL cells. RESULTS Compared with their circulating counterparts, airway eosinophils had decreased CCR3 and increased CCR4, CCR9, and CXCR3 expression on their cell surface. Furthermore, expression of CCR3, CCR4, and CXCR3 was significantly correlated with the percentage of eosinophils in BAL fluid at 48 hours. Eosinophils also expressed CXCR4, but this receptor did not change after antigen-induced recruitment to the airway. In contrast, the expression of CCR1, CCR2, CCR5, CCR6, CCR7, CXCR1, and CXCR2 remained undetectable on either blood or BAL eosinophils. CONCLUSIONS Our data suggest that recruitment of eosinophils to the airway is associated with a modulation of their chemokine receptor profiles. These changes in chemokine receptors could be involved in determining eosinophil function and antigen-induced airway inflammation.

Human Airway Eosinophils Respond to Chemoattractants with Greater Eosinophil-Derived Neurotoxin Release, Adherence to Fibronectin, and Activation of the Ras–ERK Pathway When Compared with Blood Eosinophils

Human blood eosinophils exposed ex vivo to hematopoietic cytokines (e.g., IL-5 or GM-CSF) subsequently display enhanced responsiveness to numerous chemoattractants, such as chemokines, platelet-activating factor, or FMLP, through a process known as priming. Airway eosinophils, obtained by bronchoalveolar lavage after segmental Ag challenge, also exhibit enhanced responsiveness to selected chemoattractants, suggesting that they are primed during cell trafficking from the blood to the airway. Earlier work has shown that chemoattractants stimulate greater activation of ERK1 and ERK2 following IL-5 priming in vitro, thus revealing that ERK1/ERK2 activity can be a molecular readout of priming under these circumstances. Because few studies have examined the intracellular mechanisms regulating priming as it relates to human airway eosinophils, we evaluated the responsiveness of blood and airway eosinophils to chemoattractants (FMLP, platelet-activating factor, CCL11, CCL5, CXCL8) with respect to degranulation, adherence to fibronectin, or Ras–ERK signaling cascade activation. When compared with blood eosinophils, airway eosinophils exhibited greater FMLP-stimulated eosinophil-derived neurotoxin release as well as augmented FMLP- and CCL11-stimulated adherence to fibronectin. In airway eosinophils, FMLP, CCL11, and CCL5 stimulated greater activation of Ras or ERK1/ERK2 when compared with baseline. Ras activation by FMLP in blood eosinophils was also enhanced following IL-5 priming. These studies are consistent with a model of in vivo priming of eosinophils by IL-5 or related cytokines following allergen challenge, and further demonstrate the key role of priming in the chemoattractant-stimulated responses of eosinophils. These data also demonstrate the importance of the Ras–ERK signaling pathway in the regulation of eosinophil responses to chemoattractants in the airway. Human airway eosinophils respond to several chemoattractants with increased activation of the Ras–ERK cascade, eosinophil-derived neurotoxin release, and adherence to fibronectin relative to blood eosinophils.

Potential contribution of IL-7 to allergen-induced eosinophilic airway inflammation in asthma.

The primary function of IL-7 is to promote maturation and survival of T cells. Through microarray expression analysis, we previously observed that human blood eosinophils express mRNA for IL-7Rα (CD127) and its common γ chain (CD132). The purpose of this study was to determine whether eosinophils have functional IL-7 receptors and to assess the potential contribution of IL-7 to eosinophilic airway inflammation by evaluating its presence in bronchoalveolar lavage (BAL) fluid of subjects with atopic asthma before and after segmental bronchoprovocation with allergen. Immunoblot analysis revealed that CD127 is present in highly purified human blood eosinophils. Furthermore, eosinophils responded to IL-7 with phosphorylation of STAT5, up-regulation of the activation marker CD69, and prolonged survival. Neutralization of GM-CSF but not IL-5 significantly blunted these functional responses, suggesting that IL-7 mediates its effects by promoting eosinophil release of autologous GM-CSF. Notably, the suppressive effect of anti-GM-CSF on STAT5 phosphorylation occurred within 10 min of eosinophil exposure to IL-7. Thus, IL-7 likely activates eosinophil release of preformed rather than newly synthesized GM-CSF. The biological relevance of IL-7 to eosinophilia in vivo was implicated in a study of airway allergen challenge in patients with allergic asthma. IL-7 concentrations in BAL fluid increased significantly 48 h after segmental allergen challenge and were highly correlated with BAL eosinophils (r = 0.7, p < 0.001). In conclusion, the airway response to allergen is associated with the generation of IL-7, which may contribute to airway inflammation by promoting enhanced eosinophil activation and survival. Activation of eosinophils is a novel function for IL-7.

Identification of Genes Expressed by Human Airway Eosinophils after an In Vivo Allergen Challenge

Background The mechanism for the contribution of eosinophils (EOS) to asthma pathophysiology is not fully understood. Genome-wide expression analysis of airway EOS by microarrays has been limited by the ability to generate high quality RNA from sufficient numbers of airway EOS. Objective To identify, by genome-wide expression analyses, a compendium of expressed genes characteristic of airway EOS following an in vivo allergen challenge. Methods Atopic, mild asthmatic subjects were recruited for these studies. Induced sputum was obtained before and 48h after a whole lung allergen challenge (WLAC). Individuals also received a segmental bronchoprovocation with allergen (SBP-Ag) 1 month before and after administering a single dose of mepolizumab (anti-IL-5 monoclonal antibody) to reduce airway EOS. Bronchoalveolar lavage (BAL) was performed before and 48 h after SBP-Ag. Gene expression of sputum and BAL cells was analyzed by microarrays. The results were validated by qPCR in BAL cells and purified BAL EOS. Results A total of 299 transcripts were up-regulated by more than 2-fold in total BAL cells following SBP-Ag. Mepolizumab treatment resulted in a reduction of airway EOS by 54.5% and decreased expression of 99 of the 299 transcripts. 3 of 6 post-WLAC sputum samples showed increased expression of EOS-specific genes, along with the expression of 361 other genes. Finally, the intersection of the 3 groups of transcripts (increased in BAL post SBP-Ag (299), decreased after mepolizumab (99), and increased in sputum after WLAC (365)) was composed of 57 genes characterizing airway EOS gene expression. Conclusion We identified 57 genes that were highly expressed by BAL EOS compared to unseparated BAL cells after in vivo allergen challenge. 41 of these genes had not been previously described in EOS and are thus potential new candidates to elucidate EOS contribution to airway biology.

Semaphorin 7A is expressed on airway eosinophils and upregulated by IL-5 family cytokines

Semaphorin 7A (sema7a) plays a major role in TGF-β1-induced lung fibrosis. Based on the accumulating evidence that eosinophils contribute to fibrosis/remodeling in the airway, we hypothesized that airway eosinophils may be a significant source of sema7a. In vivo, sema7a was expressed on the surface of circulating eosinophils and upregulated on bronchoalveolar lavage eosinophils obtained after segmental bronchoprovocation with allergen. Based on mRNA levels in unfractionated and isolated bronchoalveolar cells, eosinophils are the predominant source of sema7a. In vitro, among the members of the IL-5-family cytokines, sema7a protein on the surface of blood eosinophils was increased more by IL-3 than by GM-CSF or IL-5. Cytokine-induced expression of cell surface sema7a required translation of newly synthesized protein. Finally, a recombinant sema7a induced alpha-smooth muscle actin production in human bronchial fibroblasts. semaphorin 7A is a potentially important modulator of eosinophil profibrotic functions in the airway remodeling of patients with chronic asthma.

Potent synergistic effect of IL-3 and TNF on matrix metalloproteinase 9 generation by human eosinophils

TNF (designated as TNF-α under previous nomenclature) is the preeminent activator of MMP-9 generation from a variety of cells including eosinophils. We have previously established that TNF strongly synergizes with IFN-γ and IL-4 for eosinophil synthesis of Th1- and Th2-type chemokines respectively. Thus, we sought to determine if TNF-induced synthesis of MMP-9 would be enhanced by the presence of Th1, Th2, or the eosinophil-associated common beta chain (βc) cytokines. Human blood eosinophils were cultured with TNF alone or in combination with either IFN-γ, IL-4, IL-3, IL-5, or GM-CSF. Concentrations and activities of MMP-9 in eosinophil culture supernates were measured by ELISA and gelatin zymography, mRNA transcription and stabilization by quantitative real-time PCR, and signaling events by immunoblotting and intracellular flow cytometric analysis. Individually, TNF, GM-CSF, or IL-3, but not IL-4 or IFN-γ, induced relatively small (<0.2 ng/ml) but statistically significant quantities of MMP-9. Remarkable synergistic synthesis of MMP-9 (ng/ml levels) occurred in response to TNF plus IL-3, GM-CSF or IL-5, in the order of IL-3>GM-CSF>IL-5. Zymography revealed that eosinophils release MMP-9 in its pro-form. Eosinophil stimulation with the combination of IL-3 plus TNF led to increased steady-state levels of MMP-9 mRNA, prolonged mRNA stabilization, and enhanced activation of ERK1/2 phosphorylation. Inhibition of NF-κB, MEK kinase, or p38 MAP kinase, but not JNK signaling pathways, diminished IL-3/TNF-induced MMP-9 mRNA and protein production. Thus, the synergistic regulation of eosinophil MMP-9 by IL-3 plus TNF likely involves cooperative interaction of multiple transcription factors downstream from ERK, p38, and NF-κB activation as well as post-transcriptional regulation of MMP-9 mRNA stabilization. Our data indicate that within microenvironments rich in βc-family cytokines and TNF, eosinophils are an important source of proMMP-9 and highlight a previously unrecognized role for synergistic interaction between TNF and βc-family cytokines, particularly IL-3, for proMMP-9 synthesis.