Regulation of alpha 4 integrin-mediated adhesion of human eosinophils to fibronectin and vascular cell adhesion molecule-1

Limited Dose-Dependent Effects of Vedolizumab on Various Leukocyte Subsets

OBJECTIVES

The anti-α4β7 integrin antibody vedolizumab (VDZ) is successfully used for the treatment of inflammatory bowel diseases. However, only a subgroup of patients respond to therapy. VDZ is administered at a fixed dose, leading to a wide range of serum concentrations in patients. Previous work from our group showed a dose-dependent preferential binding of VDZ to effector compared with regulatory CD4 + T cells. Therefore, we aimed to determine the dose-dependent binding profile of VDZ to other leukocyte subsets.

METHODS

We characterized α4β7 integrin expression on CD8 + T cells, CD19 + B cells, CD14 + monocytes, natural killer cells, and eosinophils from patients with inflammatory bowel disease and healthy controls. We studied the binding of VDZ to these cells at different concentrations and investigated the functional consequences for dynamic adhesion and transmigration in vitro .

RESULTS

The expression of α4β7 differed between the analyzed leukocyte subsets and was significantly higher on eosinophils from inflammatory bowel disease patients compared with controls. Almost all α4β7-expressing cells from these subsets were bound by VDZ at a concentration of 10 μg/mL. Dynamic cell adhesion was significantly impaired in all subsets, but there were no dose-dependent differences in the inhibition of adhesion.

DISCUSSION

Our data suggest that α4β7-expressing CD8 + T cells, CD19 + B cells, CD14 + monocytes, natural killer cells, and eosinophils are a target of VDZ. However, there do not seem to be concentration-dependent differences, regarding the effects on these cells in the clinically relevant range. Thus, the reported exposure-efficacy characteristic of VDZ can probably mainly be attributed to CD4 + T-cell subsets.

Eosinophils and eosinophil-associated disorders: immunological, clinical, and molecular complexity

Eosinophils and their mediators play a crucial role in various reactive states such as bacterial and viral infections, chronic inflammatory disorders, and certain hematologic malignancies. Depending on the underlying pathology, molecular defect(s), and the cytokine- and mediator-cascades involved, peripheral blood and tissue hypereosinophilia (HE) may develop and may lead to organ dysfunction or even organ damage which usually leads to the diagnosis of a HE syndrome (HES). In some of these patients, the etiology and impact of HE remain unclear. These patients are diagnosed with idiopathic HE. In other patients, HES is diagnosed but the etiology remains unknown — these patients are classified as idiopathic HES. For patients with HES, early therapeutic application of agents reducing eosinophil counts is usually effective in avoiding irreversible organ damage. Therefore, it is important to systematically explore various diagnostic markers and to correctly identify the disease elicitors and etiology. Depending on the presence and type of underlying disease, HES are classified into primary (clonal) HES, reactive HES, and idiopathic HES. In most of these patients, effective therapies can be administered. The current article provides an overview of the pathogenesis of eosinophil-associated disorders, with special emphasis on the molecular, immunological, and clinical complexity of HE and HES. In addition, diagnostic criteria and the classification of eosinophil disorders are reviewed in light of new developments in the field.

Human eosinophils constitutively express a unique serine protease, PRSS33

BACKGROUND

Eosinophils play important roles in asthma, especially airway remodeling, by producing various granule proteins, chemical mediators, cytokines, chemokines and proteases. However, protease production by eosinophils is not fully understood. In the present study, we investigated the production of eosinophil-specific proteases/proteinases by transcriptome analysis.

METHODS

Human eosinophils and other cells were purified from peripheral blood by density gradient sedimentation and negative/positive selections using immunomagnetic beads. Protease/proteinase expression in eosinophils and release into the supernatant were evaluated by microarray analysis, qPCR, ELISA, flow cytometry and immunofluorescence staining before and after stimulation with eosinophil-activating cytokines and secretagogues. mRNAs for extracellular matrix proteins in human normal fibroblasts were measured by qPCR after exposure to recombinant protease serine 33 (PRSS33) protein (rPRSS33), created with a baculovirus system.

RESULTS

Human eosinophils expressed relatively high levels of mRNA for metalloproteinase 25 (MMP25), a disintegrin and metalloprotease 8 (ADAM8), ADAM10, ADAM19 and PRSS33. Expression of PRSS33 was the highest and eosinophil-specific. PRSS33 mRNA expression was not affected by eosinophil-activating cytokines. Immunofluorescence staining showed that PRSS33 was co-localized with an eosinophil granule protein. PRSS33 was not detected in the culture supernatant of eosinophils even after stimulation with secretagogues, but its cell surface expression was increased. rPRSS33 stimulation of human fibroblasts increased expression of collagen and fibronectin mRNAs, at least in part via protease-activated receptor-2 activation.

CONCLUSIONS

Activated eosinophils may induce fibroblast extracellular matrix protein synthesis via cell surface expression of PRSS33, which would at least partly explain eosinophils' role(s) in airway remodeling.

FRNK negatively regulates IL-4-mediated inflammation

Focal adhesion kinase (FAK)-related nonkinase (PTK2 isoform 6 in humans, hereafter referred to as FRNK) is a cytoskeletal regulatory protein that has recently been shown to dampen lung fibrosis, yet its role in inflammation is unknown. Here, we show for the first time that expression of FRNK negatively regulates IL-4-mediated inflammation in a human model of eosinophil recruitment. Mechanistically, FRNK blocks eosinophil accumulation, firm adhesion and transmigration by preventing transcription and protein expression of VCAM-1 and CCL26. IL-4 activates STAT6 to induce VCAM-1 and CCL26 transcription. We now show that IL-4 also increases GATA6 to induce VCAM-1 expression. FRNK blocks IL-4-induced GATA6 transcription but has little effect on GATA6 protein expression and no effect on STAT6 activation. FRNK can block FAK or Pyk2 signaling and we, thus, downregulated these proteins using siRNA to determine whether signaling from either protein is involved in the regulation of VCAM-1 and CCL26. Knockdown of FAK, Pyk2 or both had no effect on VCAM-1 or CCL26 expression, which suggests that FRNK acts independently of FAK and Pyk2 signaling. Finally, we found that IL-4 induces the late expression of endogenous FRNK. In summary, FRNK represents a novel mechanism to negatively regulate IL-4-mediated inflammation.

PI3K is involved in β1 integrin clustering by PSGL-1 and promotes β1 integrin-mediated Jurkat cell adhesion to fibronectin

P-selectin glycoprotein ligand-1 (PSGL-1) is involved in the initial step of lymphocyte homing by interacting with P- or E-selectins expressed on activated endothelium cells. Besides, it also functions as a receptor to induce signals that increase integrin affinity to ligands and mediate cell adhesion to endothelium. Integrin is required for the second step of lymphocyte homing, whose activation has been reported tightly regulated by inside-out signals triggered by chemokines or the shear-stress generated during lymphocyte rolling on endothelium. However, the relationship between PSGL-1-triggered signals and integrin activation is not clear. In this study, we demonstrated that PSGL-1 ligation induces β1 integrin-mediated adhesion to fibronectin via regulation of both β1 subunit clustering and conformation changes. Phosphoinositide 3-kinase (PI3K) is required for PSGL-1-induced β1 integrin clustering which ultimately regulates β1 integrin-mediated Jurkat cell adhesion to fibronectin. However, PI3K is not involved in the conformation changes or increases in the total expression of β1 integrin. Taken together, we found a novel signal pathway, PSGL-1-PI3K-β1 integrin, demonstrating the cooperation between initial adhesion and subsequent arrest and stable adhesion.

Pathogenesis and classification of eosinophil disorders: a review of recent developments in the field

Eosinophils and their products play an essential role in the pathogenesis of various reactive and neoplastic disorders. Depending on the underlying disease, molecular defect and involved cytokines, hypereosinophilia may develop and may lead to organ damage. In other patients, persistent eosinophilia is accompanied by typical clinical findings, but the causative role and impact of eosinophilia remain uncertain. For patients with eosinophil-mediated organ pathology, early therapeutic intervention with agents reducing eosinophil counts can be effective in limiting or preventing irreversible organ damage. Therefore, it is important to approach eosinophil disorders and related syndromes early by using established criteria, to perform all appropriate staging investigations, and to search for molecular targets of therapy. In this article, we review current concepts in the pathogenesis and evolution of eosinophilia and eosinophil-related organ damage in neoplastic and non-neoplastic conditions. In addition, we discuss classifications of eosinophil disorders and related syndromes as well as diagnostic algorithms and standard treatment for various eosinophil-related disorders.

Lactoferrin regulates an axis involving CD11b and CD49d integrins and the chemokines MIP-1α and MCP-1 in GM-CSF-treated human primary eosinophils

Eosinophils are multifunctional immune cells that contribute to innate and adaptive immune/repair responses. Lactoferrin (LF) is an iron-binding protein indicated to alter cell adhesion and immune function by receptor-mediated interactions or by participating in redox mechanisms. The eosinophil adhesion molecules, αMβ2 and α4β1, are differentially expressed following exposure to the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) and various redox agents. We hypothesized that LF can alter the function and production of proteins involved in adhesion/migration. Utilizing eosinophil peroxidase activity or fluorescent labeling adhesion assays, LF reduced GM-CSF-induced eosinophil adhesion in the presence of fibronectin or vascular adhesion molecule-1 compared with GM-CSF treatment alone. Flow cytometric analysis of eosinophil αM (CD11b) and α4 (CD49d) integrins revealed that cotreatments (24 h) with LF plus GM-CSF induced a significant increase in CD11b compared with control and GM-CSF treatments but a significant decrease in CD49d compared with control and GM-CSF treatments. These changes in CD11b and CD49d levels were significantly correlated with the increased production of chemokines (macrophage inflammatory Protein-1α, monocyte chemotactic protein-1) and an identified increase in S100A9 production. Thus, LF release at sites of inflammation may alter eosinophil recruitment/activation and possibly the progression of diseases such as cancer and asthma where significant eosinophil influx has been described.

Biomarkers of eosinophil involvement in allergic and eosinophilic diseases: review of phenotypic and serum markers including a novel assay to quantify levels of soluble Siglec-8

There remains considerable controversy in the management of eosinophilic disorders, mainly due to a paucity of information regarding the clinical interpretation of total blood eosinophil counts versus surface activation markers versus eosinophil-derived or eosinophil-influencing mediator levels. Regrettably, few tests have been validated that define a unique clinical or prognostic phenotype that is more useful than simply monitoring total blood eosinophil counts. In this manuscript, phenotypic (cell surface) markers, along with serum and tissue-based markers that have been examined in the context of disease activity, are reviewed. We also report the development of a novel assay for detecting soluble Siglec-8 (sSiglec-8), a protein likely derived largely from eosinophils, as a potential serum biomarker. The assay consists of a competitive ELISA using a recombinant Siglec-8-Fc fusion protein. The goal of this preliminary study was to determine if sSiglec-8 is a useful biomarker that differentiates among patients with various eosinophil-associated diseases. In the final analysis, it is fair to say that further research is sorely needed to fully understand and validate the utility of various biomarkers, including sSiglec-8, before their use in clinical practice can be recommended with confidence.

Glycomic analysis of human mast cells, eosinophils and basophils

In allergic diseases such as asthma, eosinophils, basophils and mast cells, through release of preformed and newly generated mediators, granule proteins and cytokines, are recognized as key effector cells. While their surface protein phenotypes, mediator release profiles, ontogeny, cell trafficking and genomes have been generally explored and compared, there has yet to be any thorough analysis and comparison of their glycomes. Such studies are critical to understand the contribution of carbohydrates to the induction and regulation of allergic inflammatory responses and are now possible using improved technologies for detecting and characterizing cell-derived glycans. We thus report here the application of high-sensitivity mass spectrometric-based glycomics methodologies to the analysis of N-linked glycans derived from isolated populations of human mast cells, eosinophils and basophils. The samples were subjected to matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) screening analyses and MALDI-TOF/TOF sequencing studies. Results reveal substantive quantities of terminal N-acetylglucosamine containing structures in both the eosinophil and the basophil samples, whereas mast cells display greater relative quantities of sialylated terminal epitopes. For the first time, we characterize the cell surface glycan structures of principal allergic effector cells, which by interaction with glycan-binding proteins (e.g. lectins) have the possibility to dictate cellular functions, and might thus have important implications for the pathogenesis of inflammatory and allergic diseases.

Endothelium-derived prostaglandin I(2) controls the migration of eosinophils

BACKGROUND

Enhanced eosinophil migration from the blood into the tissue is a hallmark of allergic diseases. Prostaglandin (PG) I(2) is the major prostanoid released by endothelial cells. Mice deficient in PGI(2) receptors (IPs) show exaggerated eosinophilic inflammation in response to allergen.

OBJECTIVE

We set out to determine the role of PGI(2) in eosinophil trafficking.

METHODS

Human lung microvascular endothelial cells and purified human eosinophils were used to study adhesion and transendothelial migration. Morphologic studies were performed with fluorescence microscopy.

RESULTS

PGI(2) markedly attenuated the migration of eosinophils through cell-free filters but had no effect on neutrophil migration. The inhibitory effect of PGI(2) on eosinophils was prevented by the IP antagonist Cay10441 and the adenylyl cyclase inhibitor SQ22536. Similarly, PGI(2) prevented the adhesion of eosinophils to fibronectin and the rapid upregulation and activation of the adhesion molecule CD11b. IP expression on eosinophils was confirmed by means of flow cytometry and Western blotting. Furthermore, when endothelial cells were treated with the COX inhibitor diclofenac to abolish PGI(2) production, adhesion of eosinophils to endothelial monolayers and subsequent transendothelial migration were markedly enhanced. Similarly, the IP antagonist enhanced eosinophil adhesion to endothelial cells. Inhibition of PGI(2) biosynthesis decreased the electrical resistance of endothelial monolayers and compromised the texture of adherent junctions, as visualized by means of VE-cadherin and F-actin staining.

CONCLUSION

We propose that endothelium-derived PGI(2) might be fundamental for the maintenance of the endothelial barrier function against infiltrating cells. These results suggest that selective IP agonists might have beneficial effects in allergic inflammation.

Eosinophil-selective binding and proapoptotic effect in vitro of a synthetic Siglec-8 ligand, polymeric 6'-sulfated sialyl Lewis x

The lectin Siglec-8 (sialic acid-binding, immunoglobulin-like lectin), which is selectively expressed on eosinophil surfaces and regulates eosinophil survival, preferentially binds to the glycan 6'-sulfo-sialyl Lewis X (6'-sulfo-sLe(x)). Antibody engagement of Siglec-8 on eosinophils causes their apoptosis, suggesting that engagement of Siglec-8 with its natural glycan ligands in vivo may control allergic inflammation. We report that a soluble synthetic polymer displaying 6'-sulfo-sLe(x) glycan selectively binds to human eosinophils and human embryonic kidney 293 cells expressing Siglec-8. Binding was inhibited by anti-Siglec-8 antibody. In whole blood, eosinophils were the only leukocyte subtype to detectably bind polymeric 6'-sulfo-sLe(x). Interleukin-5-primed eosinophils underwent apoptosis when incubated with either anti-Siglec-8 monoclonal antibody or polymeric 6'-sulfo-sLe(x), although the glycan polymer was less effective. These data demonstrate that a soluble, multivalent glycan selectively binds to human eosinophils and induces their apoptosis in vitro and provide proof-of-concept that such a reagent could be used to selectively target eosinophils.

The extracellular matrix protein mindin regulates trafficking of murine eosinophils into the airspace

Asthma remains a major cause of morbidity and hospitalizations in developed nations. Despite the widespread prevalence of this disease, the genetic and environmental factors that mediate development and progression of allergic airways disease remain poorly understood. Pulmonary recruitment of eosinophils is believed to contribute to many cardinal features of allergic airways disease. Therefore, it is paramount to understand host factors that contribute to pulmonary eosinophil recruitment into the lungs. Mindin is a component of pulmonary extracellular matrix, which can regulate inflammatory cell recruitment. We characterized the role of mindin in the severity of allergic airways disease using established murine models. There were no baseline differences in wild-type and mindin-deficient animals in cell counts or airway physiology. Using the OVA murine model of allergic airways disease, we observed that mindin-deficient animals have less-severe allergic airways disease with fewer airspace eosinophils and lower lung-lavage levels of inflammatory Th2 cytokines such as IL-13 and IL-4. Furthermore, mindin-deficient animals have reduced airway hyper-responsiveness after methacholine challenge. To determine the role of mindin in eosinophil trafficking, independent of antigen immunization or T lymphocyte activation, we instilled IL-13 directly into the lungs of mice. In this model, mindin regulates eosinophil recruitment into the airspace. In vitro experiments demonstrate that mindin can enhance eotaxin-mediated eosinophil adhesion and migration, which are dependent on the expression of integrins alphaMbeta2 and alpha4beta1. In conclusion, these data suggest that mindin participates in integrin-dependent trafficking of eosinophils and can contribute to the severity of allergic airways disease.

Homeostatic intracellular-free Ca2+ is permissive for Rap1-mediated constitutive activation of alpha4 integrins on eosinophils

Although much progress has been made in understanding the molecular mechanisms underlying agonist-induced "inside-out" activation of integrins, little is known about how basal levels of integrin function are maintained. This is particularly important for nonactivated eosinophils, where intermediate activation of alpha(4)beta(1) integrin supports recruitment to endothelial cells under flow conditions. Depletion of intracellular Ca(2+) and pharmacological inhibition of phospholipase C (but not other intracellular signaling molecules, including PI3K, ERK1/2, p38 MAPK, and tyrosine kinase activity) abrogated basal alpha(4) integrin activity in nonactivated eosinophils. Basal alpha(4) integrin activation was associated with activation of the small GTPase Rap1, a known regulator of agonist-induced integrin function. Basal Rap activation was dependent upon phospholipase C, but not intracellular Ca(2+). However, depletion of intracellular Ca(2+) in CD34(+) hematopoietic progenitor cells abolished RapV12-mediated induction of alpha(4) integrin activity. Thus, residual Rap activity or constitutively active Rap activity in Ca(2+)-depleted cells is not sufficient to induce alpha(4) integrin activation. These data suggest that activation of functional alpha(4) integrin activity in resting eosinophils is mediated by Rap1 provided that the intracellular-free Ca(2+) is at a normal homeostatic concentration.

Roles of integrin activation in eosinophil function and the eosinophilic inflammation of asthma

Eosinophilic inflammation is a characteristic feature of asthma. Integrins are highly versatile cellular receptors that regulate extravasation of eosinophils from the postcapillary segment of the bronchial circulation to the airway wall and airspace. Such movement into the asthmatic lung is described as a sequential, multistep paradigm, whereby integrins on circulating eosinophils become activated, eosinophils tether in flow and roll on bronchial endothelial cells, integrins on rolling eosinophils become further activated as a result of exposure to cytokines, eosinophils arrest firmly to adhesive ligands on activated endothelium, and eosinophils transmigrate to the airway in response to chemoattractants. Eosinophils express seven integrin heterodimeric adhesion molecules: alpha 4 beta 1 (CD49d/29), alpha 6 beta 1 (CD49f/29), alpha M beta 2 (CD11b/18), alpha L beta 2 (CD11a/18), alpha X beta 2 (CD11c/18), alpha D beta2 (CD11d/18), and alpha 4 beta 7 (CD49d/beta 7). The role of these integrins in eosinophil recruitment has been elucidated by major advances in the understanding of integrin structure, integrin function, and modulators of integrins. Such findings have been facilitated by cellular experiments of eosinophils in vitro, studies of allergic asthma in humans and animal models in vivo, and crystal structures of integrins. Here, we elaborate on how integrins cooperate to mediate eosinophil movement to the asthmatic airway. Antagonists that target integrins represent potentially promising therapies in the treatment of asthma.

A small molecule, orally active, alpha4beta1/alpha4beta7 dual antagonist reduces leukocyte infiltration and airway hyper-responsiveness in an experimental model of allergic asthma in Brown Norway rats

alpha(4)beta(1) and alpha(4)beta(7) integrins are preferentially expressed on eosinophils and mononuclear leukocytes and play critical roles in their recruitment to inflammatory sites. We investigated the effects of TR14035, a small molecule, alpha(4)beta(1)/alpha(4)beta(7) dual antagonist, in a rat model of allergic asthma. Actively sensitized rats were challenged with aerosol antigen or saline on day 21, and the responses evaluated 24 and 48-h later. TR14035 (3 mg kg(-1), p.o.) was given 1-h before and 4-h after antigen or saline challenge. Airway hyper-responsiveness to intravenous 5-hydroxytryptamine was suppressed in TR14035-treated rats. Eosinophil, mononuclear cell and neutrophil counts, and eosinophil peroxidase and protein content in the bronchoalveolar lavage fluid (BALF) were decreased in TR14035-treated rats. Histological study showed a marked reduction of lung inflammatory lesions by TR14035. At 24-h postchallenge, antigen-induced lung interleukin (IL)-5 mRNA upregulation was suppressed in TR14035-treated rats. By contrast, IL-4 levels in BALF were not significantly affected by TR14035 treatment. IL-4 selectively upregulates vascular cell adhesion molecule-1 (VCAM-1), which is the main endothelial ligand of alpha(4) integrins. Intravital microscopy within the rat mesenteric microcirculation showed that 24-h exposure to 1 microg per rat of IL-4 induced a significant increase in leukocyte rolling flux, adhesion and emigration. These responses were decreased by 48, 100 and 99%, respectively in animals treated with TR14035. In conclusion, TR14035, by acting on alpha(4)beta(1) and alpha(4)beta(7) integrins, is an orally active inhibitor of airway leukocyte recruitment and hyper-responsiveness in animal models with potential interest for the treatment of asthma.

Differential engagement of modules 1 and 4 of vascular cell adhesion molecule-1 (CD106) by integrins alpha4beta1 (CD49d/29) and alphaMbeta2 (CD11b/18) of eosinophils

We have studied adhesion of eosinophils to various forms of vascular cell adhesion molecule 1 (VCAM-1, CD106), an integrin counter-receptor implicated in eosinophil recruitment to the airway in asthma. Full-length 7d-VCAM-1, with seven immunoglobulin-like modules, contains integrin-binding sites in modules 1 and 4. The alternatively spliced six-module protein, 6d-VCAM-1, lacks module 4. In static assays, unactivated purified human blood eosinophils adhered similarly to recombinant soluble human 6d-VCAM-1 and 7d-VCAM-1 coated onto polystyrene microtiter wells. Further experiments, however, revealed differences in recognition of modules 1 and 4. Antibody blocking indicated that eosinophil adhesion to 6d-VCAM-1 or a VCAM-1 construct containing only modules 1-3, 1-3VCAM-1, is mediated by alpha4beta1 (CD49d/29), whereas adhesion to a construct containing modules 4-7, 4-7VCAM-1, is mediated by bothalpha4beta1 andalphaMbeta2 (CD11b/18). Inhibitors of phosphoinositide 3-kinase, which block adhesion of eosinophils mediated by alphaMbeta2, blocked adhesion to 4-7VCAM-1 but had no effect on adhesion to 6d-VCAM-1. Consistent with the antibody and pharmacological blocking experiments, eosinophilic leukemic cell lines lacking alphaMbeta2 did not adhere to 4-7VCAM-1 but did adhere to 6d-VCAM-1 or 1-3VCAM-1. Activation of eosinophils by interleukin (IL)-5 enhanced static adhesion to 6d-VCAM-1, 7d-VCAM-1, or 4-7VCAM-1; IL-5-enhanced adhesion to all 3 constructs was blocked by anti-alphaMbeta2. Adhesion of unstimulated eosinophils to 7d-VCAM-1 under flow conditions was inhibited by anti-alpha4 or anti-alphaM. IL-5 treatment decreased eosinophil adhesion to 7d-VCAM-1 under flow, and anti-alphaM had the paradoxical effect of increasing adhesion. These results demonstrate that alphaMbeta2 modulatesalpha4beta1-mediated eosinophil adhesion to VCAM-1 under both static and flow conditions.

Urokinase-type plasminogen activator modulates airway eosinophil adhesion in asthma

Eosinophils migrate from the vascular circulation to the inflamed airways during asthma exacerbations. While the mechanism(s) of this process is not known, the expression of urokinase-type plasminogen activator receptor (uPAR) has been found to modulate neutrophil adhesion and migration to inflammatory sites. We hypothesized that increased expression of uPAR and its ligand, uPA, enhance eosinophil adhesion in patients with asthma. Patients with allergic asthma underwent segmental bronchoprovocation with allergen; 48 h later, peripheral blood and airway (from bronchoalveolar lavage fluid) eosinophils were isolated. uPA and uPAR protein expression were measured by flow cytometry and Western blot; mRNA was quantified by real-time PCR. Eosinophil adhesion to intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 was assessed by eosinophil peroxidase activity. Airway eosinophils expressed significantly more uPA and uPAR protein and uPAR mRNA than peripheral blood eosinophils. Removal of cell-bound uPA and/or addition of exogenous uPA had no effect on blood eosinophil adhesion to ICAM-1 or VCAM-1. In contrast, exogenous uPA stimulated ICAM and VCAM adhesion of airway eosinophils. N-formyl-methionyl-leucyl-phenylalanine-activated airway eosinophil adherence to VCAM-1 and ICAM-1 (VCAM-1, 52.8 +/- 4.7%; ICAM-1, 49.2 +/- 5.3%) was increased over blood eosinophil adhesion (VCAM-1, 38.4 +/- 3.6%; ICAM-1, 27.7 +/- 4.9%; P < 0.05). Removal of cell-bound uPA from airway eosinophils decreased adhesion to blood cell levels; reintroduction of exogenous uPA completely restored adhesion levels. These data suggest that constitutive uPA primes, and exogenous uPA can activate, airway eosinophil adhesion following segmental allergen challenge and that increased uPA expression may be a mechanism of increased eosinophil infiltration and function in asthma.

Dissection of the hyperadhesive phenotype of airway eosinophils in asthma

Asthma is characterized by appearance of eosinophils in the airway. Eosinophils purified from the airway 48 h after segmental antigen challenge are described as exhibiting greater adhesion to albumin-coated surfaces via an unidentified beta2 integrin and increased expression of alphaMbeta2 (CD11b/18) compared with purified blood eosinophils. We have investigated the determinants of this hyperadhesive phenotype. Airway eosinophils exhibited increased reactivity with the CBRM1/5 anti-alphaM activation-sensitive antibody as well as enhanced adhesion to VCAM-1 (CD106) and diverse ligands, including albumin, ICAM-1 (CD54), fibrinogen, and vitronectin. Purified blood eosinophils did not adhere to the latter diverse ligands. Enhanced adhesion of airway eosinophils was blocked by anti-alphaMbeta2. Podosomes, structures implicated in cell movement and proteolysis of matrix proteins, were larger and more common on airway eosinophils adherent to VCAM-1 when compared with blood eosinophils. Incubation of blood eosinophils with IL-5 replicated the phenotype of airway eosinophils. That is, IL-5 enhanced recognition of alphaM by CBRM1/5; stimulated alphaMbeta2-mediated adhesion to VCAM-1, albumin, ICAM-1, fibrinogen, and vitronectin; and increased podosome formation on VCAM-1. Thus, the hyperadhesion of airway eosinophils after antigen challenge is mediated by upregulated and activated alphaMbeta2.

Eosinophil function in allergic inflammation: from bone marrow to tissue response

The role of the eosinophil in the pathophysiology of allergy and asthma has been the focus of intense interest during the past two decades. Although the presence of eosinophils in humans with allergy and asthma is well established, the precise role of this cell in human and animal tissue response is still unclear. However, recent developments in research on many organ systems have provided novel insights into the possible underlying role of the eosinophil in both allergic and nonallergic inflammation. In this review, we examine the pathways associated with eosinophil recruitment and activation, and discuss these findings with reference to clinically defined categories.

Extremely rapid and intense induction of apoptosis in human eosinophils by anti-CD30 antibody treatment in vitro

Apoptosis is an important cellular mechanism for controlling cell viability and proliferation. With respect to eosinophils, cytokines prolong their survival, whereas corticosteroids reduce their survival in vitro. CD30, a member of the TNFR family, is expressed on the surface of many cell types, including Hodgkin's lymphoma cells. CD30 is capable of inducing apoptosis after Ab treatment in some cell lines. To determine whether this surface structure is involved in apoptosis of human eosinophils, we examined its expression and the effect of anti-CD30 Ab treatment on the viability of eosinophils. Purified human eosinophils expressed low, but consistently detectable, levels of CD30. Immobilized, but not soluble, forms of anti-CD30 Abs (HRS-4 and Ber-H8) or recombinant mouse CD30 ligand exhibited an extremely rapid and intense survival-reducing effect on the eosinophils in the presence of exogenous IL-5; this effect was both concentration and time dependent. Furthermore, high concentrations of IL-5 could not reverse the reduced survival rates. After treatment with anti-CD30 Ab, gel electrophoresis of DNA extracted from the eosinophils demonstrated changes consistent with apoptosis. The immobilized F(ab')(2) of the anti-CD30 Ab failed to induce eosinophil apoptosis. The addition of anti-CD18 Ab also completely abrogated the induction of eosinophil apoptosis. Further examination using specific signal transduction inhibitors suggested the involvement of p38, mitogen-activated protein kinase kinase 1/2, and specific tyrosine kinase, but not NF-kappaB, in the induction of CD30-mediated eosinophil apoptosis. These data demonstrate that CD30 can modify eosinophil survival by causing an extremely rapid and intense induction of apoptosis through a tightly regulated intracellular signaling pathway.

The strength of the OVA-induced airway inflammation in rats is strain dependent

To examine the influence of genetics on the OVA-induced allergic inflammatory response in lungs we compared rats that are genetically Th2-predisposed (Brown Norway, inbred) or not genetically predisposed (Sprague Dawley, outbred). Rats were sensitized with ovalbumin (OVA) and challenged four weeks later with OVA aerosol. Eighteen hours after challenge, lung tissue was studied for evaluation of numbers of eosinophils, neutrophils, macrophages and mast cells, as well as for expression of P-selectin, E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells. From a separate portion of the pulmonary tissue, leucocytes were isolated to analyse numbers of IFNgamma and IL-4 producing cells (ELISPOT assay) and frequencies of T-cell subsets and B cells. We found increased numbers of eosinophils and neutrophils in the lung, an increased number of IL-4 producing cells in lung cell isolates and increased levels of serum (OVA- specific)-IgE in both rat strains. In addition, expression of E-selectin and ICAM-1 was up regulated in both rat strains whereas expression of VCAM-1 was only up regulated in the BN rat. Although the 'allergic' Th2 response to OVA was detectable in both rat strains, it was more pronounced in the BN rat than in the SD rat. However, the SD rat, which is not predisposed to respond in either a Th2 or Th1-like way, appeared capable of mounting an allergic response to OVA. This suggests that other factors than genetic contribute to allergic disease.

Mechanisms of eosinophil recruitment and activation

The role of the eosinophil in the pathophysiology of allergy and asthma has been the focus of intense interest during the last two decades. While the presence of eosinophils in humans with allergy and asthma is well established, the precise role of this cell in humans and in animal models is less clear. However, recent developments in research on many organ systems have provided novel insights into the possible underlying role of the eosinophil in both allergic and nonallergic inflammation. This review examines the pathways associated with eosinophil recruitment and activation and discusses these findings, with reference to clinically defined categories.

Extracellular signal-regulated kinase 1/2-mediated phosphorylation of cytosolic phospholipase A2 is essential for human eosinophil adhesion to fibronectin

We examined the role of p38, p42, and p44 mitogen-activated protein kinase (MAPK) isoforms and cytosolic phospholipase A(2) (cPLA(2)) activation in human eosinophil adhesion to plate-coated fibronectin (FN). In the control state, eosinophil adhesion was maximal, with 10 microg/ml FN at 30 min, and decreased after 60-90 min. Western blot analysis demonstrated that p44/42 MAPK (extracellular signal-regulated kinase (ERK)1/2) and cPLA(2) were phosphorylated during adhesion to FN, whereas p38 MAPK phosphorylation was unchanged. Preincubation of eosinophils with U0126 or PD98059, two structurally unrelated MAPK kinase inhibitors, or arachidonic trifluoromethyl ketone, a cPLA(2) inhibitor, blocked eosinophil adhesion to FN. By contrast, eosinophil adhesion was unaffected by SB203580, a p38 MAPK inhibitor. Pretreatment of eosinophils with okadaic acid, a serine/threonine phosphatase inhibitor, at the concentrations that induced ERK1/2 and cPLA(2) phosphorylation caused an increase in maximal eosinophil adhesion to FN for >60 min. MAPK kinase inhibition but not p38 inhibition also blocked FN-mediated F-actin redistribution in eosinophils and prevented cPLA(2) phosphorylation caused by adhesion to FN. These results demonstrate that ERK1/2 mediating cPLA(2) activation is essential for eosinophil adhesion to FN.

Eotaxin induces a sustained reduction in the functional adhesive state of very late antigen 4 for the connecting segment 1 region of fibronectin

BACKGROUND

Eosinophils that have bound to extracellular matrix proteins, such as the connecting segment 1 (CS-1) region of fibronectin, need to deadhere before undergoing chemotaxis through the extracellular matrix.

OBJECTIVE

We have investigated whether eotaxin can regulate the strength of eosinophil adhesion to the CS-1 region of fibronectin.

METHODS

We have used a micropipette single-cell adhesion assay to determine the force of eosinophil adhesion to the CS-1 region of fibronectin.

RESULTS

Eosinophils bound to CS-1 with high avidity, and this binding could be inhibited with neutralizing antibodies to alpha4 integrins expressed by eosinophils or with neutralizing antibodies to CS-1. Eosinophils incubated in the presence of eotaxin demonstrated a transient increase in the force of eosinophil adhesion to CS-1, which was followed by a more sustained reduction in the force of eosinophil adhesion to CS-1, as assessed in the micropipette single-cell adhesion assay. This decreased binding of eosinophils to CS-1 was not due to alterations in very late antigen 4 (VLA-4) receptor number, as assessed with FACS analysis, or alterations in VLA-4 receptor distribution, as assessed with immunofluorescence microscopy.

CONCLUSIONS

These studies suggest that eotaxin can cause a transient increase followed by a more sustained reduction in the functional force of VLA-4 adhesion to CS-1 and thus promote deadhesion of CS-1 adherent eosinophils in the extracellular matrix.

Hydrogen peroxide augments eosinophil adhesion via beta2 integrin

During eosinophil (EOS) accumulation at sites of allergic inflammation, an initial step is the binding of EOS to adhesion molecules expressed on vascular endothelial cells (EC). We have previously observed that adhesion of peripheral blood EOS to recombinant human vascular cell adhesion molecule-1 (rh-VCAM-1) stimulates the respiratory burst of EOS. Although the biological consequence of this activation remains to be elucidated, reactive oxygen species such as hydrogen peroxide (H2O2) may modify the adhesive property of EOS. In the present study, we examined whether H2O2 modifies the adhesive property of EOS. EOS were isolated from the peripheral blood of healthy subjects. Adhesion of the EOS to paraformaldehyde-fixed human umbilical vein EC (HUVEC), stimulated or not stimulated with tumour necrosis factor-alpha (TNF-alpha; 100 pM for 24 hr), was examined in the presence or absence of H2O2. H2O2 significantly enhanced adhesion of EOS to both resting and TNF-alpha-stimulated fixed HUVEC (P < 0.01, respectively). Such enhancing effects were inhibited by anti-beta2 integrin antibody or anti-CD11b antibody, but not by anti-CD11a or anti-alpha4 integrin antibody. H2O2 also enhanced EOS adhesion to rh-intracellular cell adhesion molecule-1 (ICAM-1) but not to rh-VCAM-1. Finally, H2O2 enhanced the expression of both CD11b and CD18 on EOS. These results indicate that H2O2 directly augments the adhesive property of EOS through beta2 integrin.

Selective upregulation of a functional beta7 integrin on differentiating eosinophils

BACKGROUND

The sequence of adhesion-molecule expression during eosinophil differentiation remains unclear.

METHODS

We analyzed the surface expression of alpha4, beta1, and beta7 integrins and compared it to established myeloid developmental markers, using the eosinophilic cell line HL-60 clone 15, as well as cord and peripheral blood differentiation assays.

RESULTS

Cells induced to eosinophil differentiation by treatment with butyric acid, IL-5, and GM-CSF showed a significant upregulation of beta7 integrin expression coincident with a marked upregulation of CD35 and attenuation of CD33 and beta1 integrin expression. In addition, adhesion of induced HL-60 clone 15 cells to fibronectin was attenuated by a beta7 integrin antibody.

CONCLUSIONS

Our data show that protein synthesis-dependent upregulation of the functional beta7 integrin occurs under conditions when beta4 and beta1 integrins are fully expressed, indicating a sequential appearance of specific adhesion molecules on differentiating eosinophil progenitors.

CCR3-active chemokines promote rapid detachment of eosinophils from VCAM-1 in vitro

Selective eosinophil recruitment is the result of orchestrated events involving cell adhesion molecules, chemokines, and their receptors. The mechanisms by which chemokines regulate eosinophil adhesion and migration via integrins are not fully understood. In our study, we examined the effect of CCR3-active chemokines on eosinophil adhesion to VCAM-1 and BSA under both static and flow conditions. When eotaxin-2 or other CCR3-active chemokines were added to adherent eosinophils, it induced rapid and sustained eosinophil detachment from VCAM-1 in a concentration-dependent manner. Adhesion was detectably reduced within 3 min and was further reduced at 10-60 min. Simultaneously, eotaxin-2 enhanced eosinophil adhesion to BSA. Preincubation of eosinophils with the CCR3-blocking mAb 7B11 completely prevented chemokine-induced changes in adhesion to VCAM-1 and BSA. Using a different protocol, pretreatment of eosinophils with chemokines for 0-30 min before their use in adhesion assays resulted in inhibition of VCAM-1 adhesion and enhancement of BSA adhesion. By flow cytometry, expression of alpha4 integrins and a beta1 integrin activation epitope on eosinophils was decreased by eotaxin-2. In a flow-based adhesion assay, eotaxin-2 reduced eosinophil accumulation and the strength of attachment to VCAM-1. These results show that eotaxin-2 rapidly reduced alpha4 integrin function while increasing beta2 integrin function. These findings suggest that chemokines facilitate migration of eosinophils by shifting usage away from beta1 integrins toward beta2 integrins.

Regulation of the release of eosinophil cationic protein by eosinophil adhesion

BACKGROUND

Varying release of eosinophil granule proteins depending on the stimulus and environmental factors has previously been reported.

OBJECTIVE

To investigate the degranulation from adherent eosinophils by using mixed granulocytes.

METHODS

Granulocytes isolated by Percoll gradient centrifugation were incubated on plates coated with plasma and tissue fibronectin, fibrinogen or human serum albumin (HSA) and stimulated with Mn2+, phorbol-myristate-acetate (PMA), formyl-methionyl-leucyl-phenylalanine (f-MLP) and combinations thereof, respectively. The release of eosinophil cationic protein (ECP) was measured by radioimmunoassay.

RESULTS

Unstimulated eosinophils incubated in wells coated with plasma and tissue fibronectin, fibrinogen or HSA did not release any ECP. Furthermore, Mn2+ (5 mmol/L) did not induce release of ECP despite the fact that adhesion of eosinophils to these four proteins was induced. PMA stimulated a dose-dependent release of ECP. Contemporaneous stimulation of eosinophils with PMA and Mn2+ induced a dramatically increased release of ECP regardless of which protein the eosinophils were adhering to. A small but significant release of ECP was found when eosinophils incubated on plates coated with fibrinogen and HSA were stimulated by f-MLP. Contemporaneous stimulation of eosinophils with f-MLP and Mn2+ did not induce any synergistic effect on the release of ECP. On the contrary, Mn2+ inhibited the release of ECP induced by f-MLP from eosinophils. Serum-opsonized Sephadex particles stimulated a potent increase of the release of ECP up to 12%-14% in the presence of plasma fibronectin and, in particular, fibrinogen. The kinetics of eosinophil adhesion and degranulation showed that the cellular adhesion preceded the degranulation response and that the degranulation patterns depend on the stimuli and environment.

CONCLUSION

The present study indicated that cellular adhesion plays an important role in the regulation of eosinophil degranulation, but that adhesion and degranulation can be induced separately.

VCAM-1 is more effective than MAdCAM-1 in supporting eosinophil rolling under conditions of shear flow

The ability of the 4 integrin counterligands vascular cell adhesion molecule (VCAM)-1 or mucosal addressin (MAd)CAM-1 to support eosinophil rolling or firm adhesion under conditions of physiologic flow has not been delineated. Using a parallel plate flow chamber in vitro and intravital microscopy in vivo, we demonstrate that eosinophil rolling and adhesion on VCAM-1 is mediated by both 4β1 and 4β7 integrins. Eosinophils rolled equally efficiently on both VCAM-1 2 domain and VCAM-1 7 domain, suggesting that the N-terminal 2 domains of VCAM-1 are sufficient to support eosinophil rolling under conditions of flow. Furthermore, activation of the eosinophil β1 integrin with monoclonal antibody (mAb) 8A2 resulted in both resistance to shear stress–induced detachment from VCAM-1 in vitro and in stable arrest of rolling eosinophils on interleukin (IL)-1β–stimulated venules in vivo. Eosinophils rolled less efficiently on MAdCAM-1– than on VCAM-1–coated coverslips under conditions of flow. However, eosinophils firmly adhered as efficiently to MAdCAM-1 as to VCAM-1. Overall, these results demonstrate that both VCAM-1 and MAdCAM-1 can support eosinophil firm adhesion under conditions of flow. In contrast, VCAM-1 is significantly more efficient than MAdCAM-1 in supporting eosinophil rolling under conditions of flow.

Advances in the immunobiology of eosinophils and their role in disease

Eosinophils play a protective role in host immunity to infections by parasitic worms and, detrimentally, are involved in the pathophysiology of asthma and other allergic diseases. Airway inflammation is central to the pathology of asthma and is characterized by infiltration of the bronchial mucosa by large numbers of proinflammatory cells, amongst which the eosinophil is prominent despite being a minority constituent of circulating leukocytes. Crucial steps in eosinophilic inflammation include augmented production of eosinophils in the bone marrow, their increased release into the circulation, and their selective accumulation in the conducting airways. The eosinophil has a potent armory of proinflammatory mediators, including cytotoxic granule proteins, cytokines and lipid mediators with considerable potential to initiate and sustain an inflammatory response. Thus there is much interest in the elucidation of the mechanisms responsible for eosinophil accumulation, persistence, activation and ultimate fate. This article reviews our current understanding of the role of the eosinophil in human disease and the immunobiology of this important proinflammatory cell.

Methods for simultaneous quantitative analysis of eosinophil and neutrophil adhesion and transmigration

Granulocytes play important roles in various inflammatory responses. The aim of this study was to develop in vitro methods to enable simultaneous analysis of eosinophil and neutrophil adhesion and transmigration in mixed granulocyte preparations. We used fibronectin-coated plates, with or without semipermeable inserts, to measure adhesion and transmigration. Granulocytes, from healthy blood donors, were stimulated with either interleukin (IL)-5 and eotaxin or N-formyl-methionyl-leucyl-phenylalanine (fMLP), during incubation in the wells. Three different detergents: n-octyl-beta-D-glucopyranoside (OG), Triton-X-100 or N-cetyl-N,N, N-trimethylammonium bromide (CTAB), were tested for their ability to cause lysis of granulocytes with minimal effect on eosinophil cationic protein (ECP) and myeloperoxidase (MPO) antigenicity. These two proteins were used for quantitative analysis of eosinophil and neutrophil adhesion/transmigration, and CTAB was the most efficient lysing reagent. Cell-recovery rates, based on ECP/MPO measurements, were > 95% in both assays. The adhesion and transmigration of eosinophils increased in a time-dependent manner upon stimulation with IL-5 and eotaxin. Eosinophil adhesion reached a plateau at 90 min of incubation and transmigration at 240 min. Neutrophils displayed a similar pattern of adhesion and transmigration upon activation with fMLP, reaching respective plateaux at 30 and 90 min. Our study shows that CTAB is an effective detergent for lysing granulocytes, yielding high and reproducible recovery rates of ECP and MPO. Measurement of ECP and MPO, as markers for cell counts, can therefore be used to quantify adhesive and transmigration properties of eosinophils and neutrophils in mixed granulocyte populations.

A Comparison of C3a and C5a-Mediated Stable Adhesion of Rolling Eosinophils in Postcapillary Venules and Transendothelial Migration In Vitro and In Vivo

The comparative ability of the complement anaphylatoxins C3a and C5a to mediate leukocyte adhesion and transendothelial migration in vivo and in vitro was investigated. Superfusion of IL-1β-stimulated rabbit mesentery with C3a resulted in a rapid and stable adhesion of rolling eosinophils, but not neutrophils, to postcapillary venules. However, C3a failed to evoke subsequent transmigration of the adherent eosinophils. In contrast, C5a induced both the rapid activation-dependent firm adhesion and transmigration of eosinophils and neutrophils through venular endothelium. C3a induced selective shedding of L-selectin and an increase in αMβ2 integrin expression on eosinophils but not neutrophils, while C5a induced shedding of L-selectin and up-regulation of αMβ2 integrin on both eosinophils and neutrophils. Both C3a- and C5a-dependent adhesion to venular endothelium was blocked by ex vivo treatment of eosinophils with anti-α4 and anti-β2 integrin mAbs. In vitro, both C3a (but not C3adesArg) and C5a (including C5adesArg)-dependent transmigration of eosinophils across IL-1β-stimulated endothelial monolayer was mediated by α4β1 and αMβ2 integrins. Overall these studies suggest that C3a is eosinophil-specific chemotactic mediator that influences selectively eosinophil adhesion but not transmigration in vivo. C5a in contrast is a complete activator of integrin-dependent adhesion as well as transmigration of eosinophils and neutrophils.

alphadbeta2 integrin is expressed on human eosinophils and functions as an alternative ligand for vascular cell adhesion molecule 1 (VCAM-1)

The beta2 family of integrins, CD11a, CD11b, CD11c, and alphad, are expressed on most leukocytes. We show that the newest member of this family, alphad, is expressed on human eosinophils in peripheral blood, and surface expression can be upregulated within minutes by phorbol ester or calcium ionophore A23187. Culture of eosinophils with interleukin 5 (IL-5) leads to a two- to fourfold increase in alphad levels by 3-7 d without a change in alpha4 integrin expression. Eosinophils isolated from late phase bronchoalveolar lavage fluids express alphad at levels similar to that seen after 3 d of IL-5 culture. Regarding alphadbeta2 ligands, in both freshly isolated and IL-5-cultured eosinophils, as well as alphadbeta2-transfected Chinese hamster ovary cells, alphadbeta2 can function as a ligand for vascular cell adhesion molecule 1 (VCAM-1). This conclusion is based on the ability of monoclonal antibodies to alphad, beta2, or VCAM-1 to block cell attachment in static adhesion assays. In experiments with eosinophils, the relative contribution of alphadbeta2 integrin- mediated adhesion is enhanced after IL-5 culture. These experiments demonstrate that alphadbeta2 is an alternative ligand for VCAM-1, and this integrin may play a role in eosinophil adhesion to VCAM-1 in states of chronic inflammation.

Expression and function of beta 1 integrins on human eosinophils

Eosinophils preferentially accumulate at sites of chronic allergic diseases such as bronchial asthma. The mechanisms by which selective eosinophil migration occurs are not fully understood. However, interactions of cell-surface adhesion molecules on the eosinophil with molecular counterligands on endothelial and epithelial cells, and on extracellular matrix proteins, are likely to be critical during the recruitment process. One possible mechanism for selective eosinophil recruitment involves the alpha-4-beta-1 (VLA-4) integrin which is not expressed on neutrophils. Correlations have been found between infiltration of eosinophils and endothelial expression of VCAM-1, the ligand for VLA-4, in the lungs of asthmatic individuals as well as in late phase reactions in the lungs, nose and skin. Epithelial and endothelial cells respond to the Th2-type cytokines IL-13 with selective de novo expression of VCAM-1, consistent with the possible role of VCAM-1/VLA-4 interactions in eosinophil influx during allergic inflammation. Both beta-1 and beta-2 integrins on eosinophils exist in a state of partial activation. For example, eosinophils can be maximally activated for adhesion to VCAM-1 or fibronectin after exposure to beta-1 integrin-activating antibodies or divalent cations, conditions that do not necessarily affect the total cell surface expression of beta-1 integrins. In contrast, cytokines like IL-5 prevent beta-1 integrin activation while promoting beta-2 integrin function. Furthermore, ligation of integrins can regulate the effector functions of the cell. For example, eosinophil adhesion via beta-1 and/or beta-2 integrins has been shown to alter a variety of functional responses including degranulation and apoptosis. Thus, integrins appear to be important in mediating eosinophil migration and activation in allergic inflammation. Strategies that interfere with these processes may prove to be useful for treatment of allergic diseases.

CD44 and CD69 represent different types of cell-surface activation markers for human eosinophils

Eosinophils (EOS) purified from peripheral blood or late-phase bronchoalveolar lavage (BAL) were analyzed with 473 monoclonal antibodies (mAbs) from the Fifth International Workshop on Human Leukocyte Antigens in an attempt to identify markers of EOS activation. Two strategies were used: (1) to look for surface markers absent on fresh EOS but present after in vivo activation (e. g., in late-phase BAL fluid [BALF]) or after in vitro culture for up to 72 h with cytokines (<= 10 ng/ml of interleukin-3 [IL-3], IL-5, or granulocyte-macrophage colony-stimulating factor [GM-CSF]); and (2) to look for markers constitutively expressed on fresh EOS that were increased after activation in vivo or after culture in vitro. With indirect immunofluorescence and flow cytometry, the first approach revealed that among approximately 350 mAbs tested, only those recognizing CD69 became bound to late-phase BALF EOS or cytokine-cultured EOS, but not to fresh EOS. Using the second approach, we observed statistically significant concentration- and time-dependent increases in CD44 expression in EOS cultured with IL-3, IL-5, or GM-CSF (approximately 2-fold increase in fluorescence intensity, P < 0.05), but not with interferon-gamma (IFN-gamma) (up to 100 ng/ml), whereas levels of 15 other constitutively expressed markers were unchanged. Despite increased expression, neither fresh nor cytokine-cultured EOS adhered to immobilized hyaluronate, a ligand for CD44. Additionally, simultaneous comparison of hypodense (specific gravity < 1.085 g/liter) and normodense (specific gravity > 1.085 g/liter) EOS from allergic donors consistently revealed higher levels of CD44 expression (approximately 3- to 8-fold) but not CD69 expression on hypodense EOS. We conclude that CD69 and CD44 represent different types of activation markers for human EOS. These findings may be useful in assessing the state of EOS activation in vitro and in vivo.

Studies of cell adhesion and flow cytometric analyses of degranulation, surface phenotype, and viability using human eosinophils, basophils, and mast cells

Products derived from eosinophils, basophils, and mast cells are considered critical to the development of allergic diseases. Studies of the selective recruitment, accumulation, and/or activation of these cells during human allergic inflammatory reactions in vitro and in vivo have been facilitated by a wide variety of methods. Some have been developed to identify and isolate these cells from a variety of sites, including blood, airway secretions, and surgical or autopsy tissues. Once enriched in purity, assays of cell adhesion to endothelium, epithelium, matrix proteins, and purified, immobilized counterligands for integrins, selectins, or immunoglobulin gene superfamily structures can be performed in vitro under both static and flow conditions. Techniques involving flow cytometry, utilizing characteristics of cellular light scatter and immunofluorescence, have permitted the elucidation of cell surface phenotype and have aided in quantification of cellular degranulation and viability. These approaches have yielded new information on the function of human eosinophils, basophils, and mast cells and have suggested unique cell-specific pathways of cell recruitment, activation, and survival that may contribute to the pathogenesis of allergic diseases.