Human eosinophils preferentially survive on tissue fibronectin compared with plasma fibronectin

In vivo neutralization of α4 and β7 integrins inhibits eosinophil trafficking and prevents lung injury during tropical pulmonary eosinophilia in mice

Integrins regulate leukocyte trafficking during homeostasis and inflammatory conditions. However, the role of α4 and β7 integrins in guiding eosinophil transmigration into the lungs during filarial manifestation of Tropical Pulmonary Eosinophilia (TPE) has not been explored. In this study, mice exhibiting TPE manifestations were administered with in vivo neutralizing antibodies against integrins α4 and β7 or their combination and immuno-pathological parameters were evaluated. Results show an intact lung barrier, significantly lower lung inflammation and reduced eosinophil counts in the Bronchoalveolar lavage fluid and lungs of mice receiving anti-α4⁺ β7 treatment. Reduced eosinophil peroxidase and β-hexosaminidase activity, downregulation of inflammatory genes, lower production of inflammatory lipid intermediates like prostaglandins E2 and D2, leukotriene B4 and cysteinyl leukotrienes were also noted in anti-α4⁺ β7 treated mice. Reduced accumulation of central memory, effector memory, regulatory T cells and lower production of IL-4, IL-5, and TGF-β were other cardinal features of anti-α4⁺ β7 treated mice lungs. Flow cytometry-sorted lung eosinophils from anti-α4⁺ β7 treated mice showed higher apoptotic potential, downregulated anti-apoptotic gene Bcl-2, and exhibited reduced F-actin polymerization and calcium influx as compared to IgG controls. In summary, neutralization of α4⁺ β7 integrins impairs the transmigration, activation and survival of eosinophils and reduces TPE induced pathology in mice lungs.

Eosinophil apoptosis and clearance in asthma

Asthma is an increasingly common respiratory condition characterized by reversible airway obstruction, bronchial hyper-responsiveness and airway inflammation with a clear unmet need for more effective therapy. Eosinophilic asthma is a phenotype of the condition that features increased blood or sputum eosinophils whose numbers correlate with disease severity. Several lines of evidence are now emerging, which implicate increased persistence of eosinophils in the lungs of patients with asthma as a consequence of inhibition of and defects in the apoptotic process, together with impaired apoptotic cell removal mechanisms. This article will update our knowledge of the mechanisms controlling eosinophil apoptosis and clearance, together with evidence implicating defects in apoptosis and pro-inflammatory cell removal in asthma. Recent developments in novel therapies for asthma that target eosinophil apoptotic and/or clearance pathways will also be discussed.

Comparative study of eosinophil chemotaxis, adhesion, and degranulation in vitro in ulcerative colitis and Crohn's disease

BACKGROUND

Eosinophils have been identified in tissues from patients with Crohn's disease (CD) and ulcerative colitis (UC) but whether they contribute to IBD pathogenesis is unknown. This study aimed to investigate the functional activity and morphological aspects of peripheral-blood eosinophils from IBD patients compared to those from healthy volunteers (HVs).

METHODS

Eosinophils from HVs and CD and UC patients were purified using a Percoll gradient and then a immunomagnetic cell separator. Functional activity in inactivated and previously activated cells was investigated by measuring adhesion to fibronectin and chemotaxis to fMLP, and degranulation was measured by release of eosinophil peroxidase (EPO). Cell morphology was investigated using electron microscopy.

RESULTS

Eosinophil adhesion to human fibronectin in both inactivated and PAF-stimulated and PMA-stimulated eosinophils was markedly higher in patients with CD than in either patients with UC or HVs. Similarly, the chemotactic response was markedly higher in eosinophils isolated from CD patients than in those isolated from UC patients or HVs. Baseline EPO release was higher in eosinophils isolated from UC patients than in those isolated from HVs or CD patients. Stimulation with fMLP or PMA did not further increase EPO release in cells from UC or CD patients. Comparable expression of MAC- 1 and VLA-4 adhesion molecules was observed on the surfaces of eosinophils from all groups, and an greater number of granules was noted in the eosinophils from UC patients than in those from CD patients.

CONCLUSIONS

Our results indicate that peripheral-blood eosinophils are potentially primed and activated in IBD patients. Whether the differences in the morphology and functional responses of eosinophil from UC and CD patients reflect differences in disease phenotype remains to be elucidated.

TNF-alpha potentiates C5a-stimulated eosinophil adhesion to human bronchial epithelial cells: a role for alpha 5 beta 1 integrin

Cooperative action of inflammatory mediators and adhesion molecules orchestrates eosinophil recruitment during allergic inflammation in the airways. This study investigated the mechanisms involved in increasing eosinophil adhesion to human bronchial epithelial cells (HBEC) following priming and activation of eosinophils with TNF-alpha and complement protein C5a, respectively. Under primed conditions, eosinophil adhesion increased 3-fold from basal (16%), and the effect was significantly greater (p < 0.05) than the increase following stimulation with C5a alone (2-fold). Eosinophil contact with HBEC was essential for priming. In contrast to C5a, adhesion of eotaxin-stimulated eosinophils to HBEC was not primed with TNF-alpha nor IL-5, a known eosinophil-priming agent. Priming caused activation of alpha(M)beta(2) integrin; mAb against either the common beta(2) integrin subunit or its ICAM-1 ligand reduced the primed component of adhesion. Using mAbs against beta(1) or alpha(5), but not alpha(4) integrin subunit, together with anti-beta(2) integrin mAb, reduced stimulated adhesion to basal levels. Cross-linking alpha(5)beta(1) integrin increased alpha(M)beta(2) integrin-dependent adhesion of eosinophils. There are no known adhesion molecule ligands of alpha(5)beta(1) integrin expressed on HBEC; however, fibronectin, the major matrix protein ligand for alpha(5)beta(1) integrin, was detected in association with HBEC monolayers. A mAb against fibronectin, in combination with anti-beta(2) integrin mAb, reduced adhesion to basal levels. In conclusion, alpha(5)beta(1) integrin may provide a contact-dependent costimulus for eosinophil priming that, together with TNF-alpha, potentiated C5a activation of alpha(M)beta(2) integrin and increased eosinophil adhesion to ICAM-1. Fibronectin, associated with HBEC, may act as a ligand for alpha(5)beta(1) integrin. Dual regulation of eosinophil priming may prevent inappropriate activation of eosinophils in the circulation.

Nasal polyposis: from cytokines to growth

Nasal polyposis (NP) is a chronic inflammatory condition that is mostly characterized by an infiltration of eosinophils. How this eosinophilic inflammation leads to polyp formation remains largely unclear. In order to identify the most important factors in polyp growth, first we report the histologic features of two early stage manifestations of eosinophilic nasal polyps compared to their surrounding normal mucosa and mature polyps from the same patients. Histomorphologic analysis of these early stage manifestations of NP showed the presence of eosinophils, forming a subepithelial cap over a pseudocyst area that was filled with albumin. In mature NP, a large pseudocyst area containing albumin was surrounded by subepithelial eosinophilia. Second, in an approach to quantify and to study possible relations between eosinophilic inflammation and changes in extracellular tissue components we measured interleukin-5 (IL-5), eotaxin, eosinophil cationic protein (ECP), leukotrienes (LTC4/D4/E4), transforming growth factor-beta 1 (TGF-beta 1), fibronectin, hyaluronic acid, and albumin in nasal tissue homogenates of 31 subjects. Nasal polyp samples (n = 16) were obtained during routine endonasal sinus surgery, whereas control non-polyp samples (n = 15) from subjects with (6) and without (9) allergic rhinitis were obtained from the inferior turbinate during septum surgery. In the group of polyp patients 11 received no treatment, whereas 5 were treated with oral glucocorticoids (GCS) within 4 weeks before surgery. IL-5 was measurable in 8 of 11 untreated NP, whereas IL-5 could not be detected in all 15 controls nor in 4 of 5 oral corticoid-treated polyps. The comparison between the untreated polyp group and controls showed significantly higher concentrations of IL-5, eotaxin, ECP, and albumin in polyp supernatants, whereas TGF-beta 1 was significantly lower. In the oral GCS-treated group, ECP and albumin were significantly reduced compared to untreated nasal polyps. The same tendency, but not reaching significance, was seen for eotaxin and fibronectin, while no difference was found for LTC4/D4/E4 and hyaluronic acid between the groups. Our observations suggest a deposition of albumin (and possibly other plasma proteins) and extracellular matrix proteins, which may be regulated by the subepithelial eosinophilic inflammation, as a possible pathogenic principle of polyp formation and growth. IL-5 and eotaxin are found to be key factors for eosinophilic accumulation and activation in NP. Oral corticoid treatment may lead to the shrinkage of NP by downregulation of the eosinophilic inflammation and reduction of the extravasation and deposition of albumin in NP.

The effect of transendothelial migration on eosinophil function

In bronchial asthma, eosinophils found in the airways have an enhanced inflammatory capacity. We hypothesized that, at least in part, changes in functional phenotype are due to the effect of transendothelial migration. To model in vivo eosinophil trafficking to the lung, we cultured human pulmonary microvascular endothelial cell (HPMEC) monolayers on Transwell filters. The HPMECs were activated with interleukin (IL)-1beta to increase cell expression of intercellular adhesion molecule (ICAM)-1 and, hence, eosinophil transmigration. Peripheral blood eosinophils from allergic patients were added to HPMEC-covered Transwell filters and incubated for 3 h at 37 degrees C. The eosinophils were collected from below (migrated cells) and above (nonmigrated cells) the HPMEC monolayer to determine surface receptor expression, in vitro survival, and oxidative burst. Eosinophils never exposed to HPMECs were used as controls. Eosinophil cell surface expression of CD69, human leukocyte-associated antigen-DR (HLA-DR), and CD54 (ICAM-1) was significantly increased after transendothelial migration through IL-1beta-treated HPMECs compared with control cells (CD69: P<0.0005; HLA-DR and CD54: P<0.05) and nonmigrated eosinophils (CD69 and HLA-DR: P<0.05). Moreover, the percent in vitro survival (48 h) of migrated eosinophils was also significantly greater (P<0.0001 by trypan blue exclusion, P< 0.05 by flow cytometry) than that of control or nonmigrated eosinophils. Prolonged survival of migrated eosinophils was inhibited by addition of anti-granulocyte macrophage colony-stimulating factor (GM-CSF) antibodies (P<0.05) to the 48-h survival culture, suggesting that autocrine production of GM-CSF was, at least partially, responsible for increased eosinophil survival. Although GM-CSF protein was not measurable in survival culture supernates, GM-CSF messenger RNA (mRNA) was expressed in both nonmigrated and migrated eosinophils but not in control cells. Similarly, the eosinophils' oxidative burst induced by platelet-activating factor, formylmethionyl leucylphenylalanine, or phorbol myristate acetate was equally, and significantly, increased in both nonmigrated and migrated eosinophils (P<0.05 versus control). Therefore, whereas exposure of eosinophils to cytokine-activated HPMECs can increase surface receptor expression, in vitro survival, GM-CSF mRNA, and the respiratory burst, transendothelial migration can further potentiate receptor expression and survival in migrated cells. These results suggest that the process of transendothelial migration selectively participates in determining the eventual phenotype of airway eosinophils.

Leukotriene receptor antagonists and synthesis inhibitors reverse survival in eosinophils of asthmatic individuals

Eosinophilia is a feature of airway inflammation associated with asthma. Leukotriene antagonists provide therapeutic benefit in asthma, but their potential antiinflammatory actions have not been fully explored. We have examined the role of eosinophil-derived cysteinyl leukotrienes in the maintenance of eosinophil survival, and the involvement of leukotrienes in the paracrine stimulation of eosinophil survival by mast cells and lymphocytes. We obtained eosinophils and autologous lymphocytes from peripheral blood of asthmatic subjects. Leukotriene (LT)-B(4), LTC(4) and LTD(4), granulocyte-macrophage colony-stimulating factor (GM-CSF), and fibronectin promoted eosinophil survival. LTD(4) (10(-)(6) M) was as effective as GM-CSF (5 ng/ml) and fibronectin (400 ng/ml) in promoting survival. Lymphocytes and conditioned medium from a human mast cell line (HMC-1) induced eosinophil survival. Blockade of cysteinyl leukotriene receptors with SKF 104353 (pobilukast, 3 nM), and inhibition of 5-lipoxygenase (5-LO) with BW A4C (1 microM) and of 5-LO activating protein with MK 886 (1 microM), all increased basal rates of eosinophil apoptosis and reversed GM-CSF-induced eosinophil survival. Fifty percent reversal of GM-CSF- induced survival was achieved with SKF 104353 at 0.3 nM. The potency of SKF 104353 was two orders of magnitude greater than that of the LTB(4) receptor antagonist SB 201146. Mast cell- and lymphocyte-induced eosinophil survival were completely reversed by SB 201146, SKF 104353, BW A4C, and MK 886. These findings provide evidence for the involvement of an autocrine cysteinyl leukotriene pathway that supports eosinophil survival in response to a range of survival stimuli. They also suggest that LTB(4) could act as a paracrine stimulus of eosinophil survival.

The impact of eotaxin- and IL-5-induced adhesion and transmigration on eosinophil activity markers

Eosinophils accumulate at sites of allergic inflammation, and play important roles in asthma/allergic disorders. The mechanism of eosinophil recruitment into tissues is not fully understood. In this study, we evaluated whether adhesion and/or transmigration, in the presence of IL-5 and eotaxin, alter the expression of CD9, CD11b, the beta1alpha4-integrin, and the EG2-epitope on intracellular ECP. We also investigated whether CD9 is involved in the adhesion process. With flow cytometry the surface expression of CD9, CD11b and the beta1alpha4-integrin, and the intracellular expression of EG2, were analyzed before, and after transmigration/adhesion to fibronectin. To evaluate the eventual role of CD9 in adhesion, eosinophils were preincubated with monoclonal antibodies to CD9. We observed decreased expression of CD9, and increased expression of CD11b on eosinophils, after adhesion and transmigration. The transmigration did not change the expression of the beta1alpha4-integrin or EG2, whereas the adhesion resulted in a decreased EG2 expression. Antibodies to CD9 decreased the adhesion property of eosinophils. The eosinophils are activated after both adhesion and transmigration by means of decreased CD9 and increased CD11b expression. The expression of the EG2-epitope on intracellular ECP was decreased when eosinophils adhered to fibronectin, probably due to degranulation. Our results also indicate that CD9 is involved in the adhesion of eosinophils to fibronectin.

Engagement of α4β7 Integrins by Monoclonal Antibodies or Ligands Enhances Survival of Human Eosinophils In Vitro

Asthma is characterized by an airway inflammatory infiltrate that is rich in eosinophilic leukocytes. Cellular fibronectin and VCAM-1, ligands for α4 integrins, are enriched in the fluid of airways of allergic patients subjected to Ag challenge. We therefore hypothesized that ligands of α4 integrins can promote eosinophil survival independent of cell adhesion. Cellular fibronectin and VCAM-1 increased viability of human peripheral blood eosinophil in a dose- and time-dependant manner whether the ligand was coated on the culture well or added to the medium at the beginning of the assay. Eosinophils cultured with cellular fibronectin were not adherent to the bottom of culture wells after 3 days. Treatment with mAb Fib 30 to β7, but not mAb P4C10 or TS2/16 to β1, increased eosinophil survival. The increased survival of eosinophils incubated with Fib 30 was blocked by Fab fragments of another anti-β7 mAb, Fib 504. Eosinophils incubated with soluble cellular fibronectin or mAb Fib 30 for 6 h demonstrated a higher level of GM-CSF mRNA than eosinophils incubated with medium alone. Addition of neutralizing mAb to GM-CSF during incubation, but not mAbs to IL-3 or IL-5, reduced the enhancement of eosinophil survival by soluble cellular fibronectin or mAb Fib 30 to control levels. Thus, viability of eosinophils incubated with cellular fibronectin or VCAM-1 is due to engagement, probably followed by cross-linking, of α4β7 by soluble ligand (or mAb) that stimulates autocrine production of GM-CSF and promotes eosinophil survival.

Resting and Cytokine-Stimulated Human Small Airway Epithelial Cells Recognize and Engulf Apoptotic Eosinophils

Eosinophils, which are prominent cells in asthmatic inflammation, undergo apoptosis and are recognized and engulfed by phagocytic macrophages in vitro. We have examined the ability of human small airway epithelial cells (SAEC) to recognize and ingest apoptotic human eosinophils. Cultured SAEC ingested apoptotic eosinophils but not freshly isolated eosinophils or opsonized erythrocytes. The ability of SAEC to ingest apoptotic eosinophils was enhanced by interleukin-1 (IL-1) or tumor necrosis factor  (TNF) in a time- and concentration-dependent fashion. IL-1 was found to be more potent than TNF and each was optimal at 10−10 mol/L, with a significant (P &lt; .05) effect observed at 1 hour postcytokine incubation that was maximal at 5 hours. IL-1 stimulation not only increased the number of SAEC engulfing apoptotic eosinophils, but also enhanced their capacity for ingestion. The amino sugars glucosamine, n-acetyl glucosamine, and galactosamine significantly inhibited uptake of apoptotic eosinophils by both resting and IL-1–stimulated SAEC, in contrast to the parent sugars glucose, galactose, mannose, and fucose. Incubation of apoptotic eosinophils with the tetrapeptide RGDS, but not RGES, significantly inhibited their uptake by both resting and IL-1–stimulated SAEC, as did monoclonal antibody against vβ3 and CD36. Thus, SAEC recognize apoptotic eosinophils via lectin- and integrin-dependent mechanisms. These data demonstrate a novel function for human bronchial epithelial cells that might represent an important mechanism in the resolution of eosinophil-induced asthmatic inflammation.

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.

Simultaneous analysis of eosinophil and neutrophil adhesion to plasma and tissue fibronectin, fibrinogen, and albumin

A simple and convenient assay for the simultaneous measurement of eosinophil and neutrophil adhesion is described. Incubations were performed in microtitre plates coated with different proteins. Adhesion of eosinophils and neutrophils was determined by the use of specific radioimmunoassays for eosinophil cationic protein (ECP) and myeloperoxidase (MPO). Using this assay, Mn2+ induced a significant increase of the adhesion of eosinophils to plasma fibronectin and fibrinogen in a time-dependent fashion, while a small increase of the adhesion of neutrophils to these two proteins was observed. In contrast, a time-dependent potent increment of the adhesion of both eosinophils and neutrophils to tissue fibronectin and albumin was found. Tissue fibronectin preferentially supported eosinophil adhesion compared with that of neutrophils in the presence of Mn2+. PMA (10(-9) mol/l) induced a significant increase in the adhesion of eosinophils and neutrophils of the same pattern to all four proteins. However, when granulocytes were stimulated by Mn2+ in combination with PMA, eosinophils and neutrophils showed different patterns of response to plasma fibronectin and fibrinogen, respectively, but the same pattern of response to tissue fibronectin. f-MLP stimulated an early increase of the adhesion of neutrophils to fibrinogen, while a weak stimulation of the adhesion of eosinophils to plasma fibronectin and fibrinogen and of neutrophils to plasma fibronectin was observed. Co-stimulation with f-MLP and Mn2+ did not induce any additive effects on granulocyte adhesion. In conclusion, the assay allows rapid quantification of eosinophil and neutrophil adhesion and can be used to directly compare the response of neutrophils and eosinophils. The assay is thus suitable for studies aimed at identifying agents with a selective effect on either of the cells.

Expression of Bcl-2 and its homologues in human eosinophils. Modulation by interleukin-5

The Bcl-2 family has been shown to be vital regulators of programmed cell death in numerous systems. To investigate the role of such proteins in the regulation of apoptosis of eosinophils, the expression of Bcl-2 and homologues Bcl-xL (death antagonists), Bax, and Bcl-xS (death agonists) were examined by immunoblot, flow cytometry, and reverse transcriptase-polymerase chain reaction analysis. Potential modulation of apoptosis-associated molecules during spontaneous apoptosis and in the presence of interleukin (IL)-5 was also investigated. Peripheral blood eosinophils were found to express constitutively Bax and Bcl-x, but Bcl-2 was absent. Analysis of mRNA revealed that the bcl-xL isoform predominated, although bcl-xS was also detectable. Spontaneous apoptosis due to culturing in the absence of cytokines for 24 h did not result in modulation of any of the Bcl-2 homologues examined. Culturing eosinophils in the presence of 100 pg/ml IL-5 for 24 h significantly reduced apoptosis (P < 0.01) to 10.7 +/- 2.6% compared with 46.8 +/- 7.4% in the absence of IL-5, and induced Bcl-2 mRNA and protein expression, with no detectable change in Bax, Bcl-x, or beta-actin as a control. This investigation indicates a specific profile of apoptotic molecules in eosinophils distinct from that of neutrophils, and indicates that survival-enhancing IL-5 modulates the expression of Bcl-2 in vitro.

Selective, tight-binding inhibitors of integrin alpha4beta1 that inhibit allergic airway responses

Integrin alpha4beta1 mediates leukocyte recruitment, activation, mediator release, and apoptosis inhibition, and it plays a central role in inflammatory pathophysiology. High-affinity, selective inhibitors of alpha4beta1, based on the Leu-Asp-Val (LDV) sequence from the alternatively spliced connecting segment-1 (CS-1) peptide of cellular fibronectin, are described that employ a novel N-terminal peptide "cap" strategy. One inhibitor, BIO-1211, was approximately 10(6)-fold more potent than the starting peptide and exhibited tight-binding properties (koff = 1.4 x 10(-4) s-1, KD = 70 pM), a remarkable finding for a noncovalent, small-molecule inhibitor of a protein receptor. BIO-1211 was also 200-fold selective for the activated form of alpha4beta1, and it stimulated expression of ligand-induced epitopes on the integrin beta1 subunit, a property consistent with occupancy of the receptor's ligand-binding site. Pretreatment of allergic sheep with a 3-mg nebulized dose of BIO-1211 inhibited early and late airway responses following antigen challenge and prevented development of nonspecific airway hyperresponsiveness to carbachol. These results show that highly selective and potent small-molecule antagonists can be identified to integrins with primary specificity for peptide domains other than Arg-Gly-Asp (RGD); they confirm the generality of integrins as small molecule targets; and they validate alpha4beta1 as a therapeutic target for asthma.

The role of alpha4 (CD49d) and beta2 (CD18) integrins in eosinophil and neutrophil migration to allergic lung inflammation in the Brown Norway rat

We investigated the role of beta2 (CD18) and alpha4 (CD49d) integrins in eosinophil and neutrophil recruitment to lung parenchyma and bronchoalveolar lavage fluid (BALF) of allergen-challenged Brown Norway (BN) rats. Challenge of sensitized BN rats with ovalbumin induced an eosinophil- and neutrophil-rich infiltrate in BALF at 24 h, accompanied by an increase in BALF protein content. Treatment with either the TA-2 monoclonal antibody (mAb) against alpha4 (as an F[ab']2 fragment) or the WT.3 mAb against beta2 integrin significantly reduced eosinophil and neutrophil accumulation in BALF by 54 to 66% and eosinophil accumulation in the parenchyma by 48%. A significant difference in effect was observed between mAb TA-2 in intact immunoglobulin G or F(ab)2 form. Combined treatment with mAbs WT.3 plus TA-2 (F[ab]2) virtually abolished eosinophil accumulation in BALF and in the parenchyma, and reduced neutrophil accumulation in BALF by 91%. In contrast, neutrophil accumulation in the lung was not inhibited by these mAb treatments. The increase in BALF protein concentration was significantly inhibited by TA-2 (by 40%) and by WT.3 plus TA-2 in combination (71% inhibition). We conclude that eosinophil and neutrophil migration into the air space in allergic lung inflammation is partially CD18 (beta2)- and CD49d (alpha4)- dependent and that alpha4 integrins mediate essentially all of the CD18-independent migration. Similarly, eosinophil accumulation in the parenchyma is completely alpha4 and CD18 (beta2) integrin-dependent. In marked contrast, neutrophil accumulation in the lung in this allergen model can occur independently of both alpha4 and beta2 integrins.

Segmental antigen challenge increases fibronectin in bronchoalveolar lavage fluid

Fibronectin may contribute to asthma pathogenesis by recruitment and activation of inflammatory cells, and by promotion of subepithelial fibrosis. Fibronectin is produced by several types of airway cells, including epithelial cells, fibroblasts, and alveolar macrophages. To test the hypothesis that antigen-induced airway inflammation is associated with increased local generation of fibronectin, segmental bronchoprovocation (SBP) with antigen and saline was performed in 17 atopic patients. Bronchoalveolar lavage (BAL) was performed at 5 min and 48 h after segmental challenge with saline or antigen. Fibronectin concentrations in BAL fluid, measured by enzyme-linked immunosorbent assay (ELISA), increased more than 5-fold 48 h after antigen challenge (65 [47 to 110] versus 407 [240 to 697] ng/ml, median and 25 to 75% interquartiles, p < 0.05). Fibronectin concentrations 48 h after antigen challenge correlated with histamine concentrations 5 min after antigen challenge and numbers of eosinophils, neutrophils, macrophages, and total cells in BAL fluid 48 h after antigen challenge. BAL was more enriched in fibronectin 48 h after challenge than would be predicted solely from increased permeability of plasma proteins. Western blot analysis showed that fibronectin in BAL fluid was largely intact and contained the extra domain-A (ED-A) splice variant of cellular fibronectin, indicative of local production. We conclude that antigen challenge in atopic subjects causes increased production of fibronectin by airway cells and speculate that this response may contribute to airway remodeling in allergic 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.

A comparative study of different methods for the assessment of apoptosis and necrosis in human eosinophils

Eosinophils, prominent cells in asthmatic inflammation, undergo apoptosis or programmed cell death following deprivation of contact with survival-promoting cytokines such as IL-5 and GM-CSF. The aim of this study was to assess a number of techniques for the quantification of apoptosis in human eosinophils cultured with or without IL-5 or GM-CSF and following staurosporine treatment. The relationship between apoptosis and necrosis in eosinophils was also determined. Eosinophils 'aged' in vitro for 48 h exhibited endonuclease DNA degradation, apoptotic morphology, increased red autofluorescence and externalisation of phosphatidylserine (PS) as assessed by binding of FITC-labelled annexin V. Annexin V-FITC binding was first detectable in eosinophils maintained at 37 degrees C for 5 h post-purification. This method proved to be the most sensitive marker of apoptosis. Morphological assessment of wet preparations of eosinophils by Kimura staining was found to be the next most-sensitive marker followed by increased red autofluorescence. The latter was a relatively insensitive method for the detection of apoptosis. At 5, 20 and 24 h of culture trypan blue exclusion indicated that eosinophil viability was high (85-90% viable cells). However, propidium iodide (PI) staining and flow cytometry revealed that, by 24 h, approximately 75% of cells had compromised membrane integrity. Eosinophils maintained in IL-5 or GM-CSF exhibited a non-apoptotic morphology and levels of annexin V-FITC binding and PI uptake similar to that of freshly isolated cells. Staurosporine (10(-5) M) treatment of eosinophils maintained in IL-5 or GM-CSF resulted in significant levels of apoptotic morphology at 2 h (23.8% +/- 6.9, p < 0.025) which was associated with negligible annexin binding. At 6 h post-staurosporine treatment significant annexin-FITC binding (38% +/- 1.5, p < 0.025) was observed compared with 93% +/- 1.2 of eosinophils displaying apoptotic morphology. Exclusion of PI demonstrated membrane integrity at all time points up to 6 h. Thus, eosinophils aged in vitro in the absence of viability-promoting cytokines exhibit evidence of both apoptosis and necrosis simultaneously. In contrast, staurosporine-treated eosinophils exhibited both membrane integrity and rapid apoptosis-associated morphological changes detected by single step Kimura staining which preceded externalisation of PS.

CD49d expression and function on allergen-stimulated T cells from blood and airway

The alpha4 chain (CD49d), which constitutes one of the chains of alpha4beta1 (very late activating antigen-4 [VLA-4]) and alpha4beta7 integrins, mediates migration of T cells to extravascular spaces. The interaction between VLA-4 and vascular cell adhesion molecule-1 (VCAM-1) has been shown to be the critical pathway for the selective accumulation of eosinophils and basophils at sites of allergic inflammation. T lymphocytes are also specifically recruited into allergic sites, including the allergic asthmatic airway. Increased numbers of activated CD4+ cells expressing the DR antigen subset of the human leukocyte antigens (HLA-DR) appear in the allergic lung 48 h after allergen inhalation. The mechanisms by which these cells localize into the lung are still unknown. We report that stimulation of allergen-specific T cells with allergen in vitro resulted in enhanced expression of alpha4 chain (CD49d) as measured by receptor density on allergen-specific T-cell lines and T-cell clones. Kinetic studies showed that CD49d density was enhanced over a 24- to 48-h period in a time-dependent fashion, and was coordinately upregulated with HLA-DR expression. We also demonstrated that increased expression of CD49d on T-cell lines 24 h and 48 h after stimulation correlated with increased adhesion to the CS-1 fragment of fibronectin. In contrast, lymphocyte function-associated antigen-1b (LFA-1b) (CD11b), LFA-3 (CD58), and intercellular adhesion molecule-1 (ICAM-1) (CD54) expression did not change with allergen stimulation. We also showed that CD49d receptor density on T cells obtained by bronchoalveolar lavage (BAL) of allergic patients before and 48 h after allergen challenge was significantly higher than that on T cells taken from BAL of normal subjects and from controls with other inflammatory lung diseases. Taken together, these findings indicate that allergen stimulation activates allergen-specific T cells and coordinately induces increased CD49d receptor expression and binding to counterligands. We postulate that allergen-driven upregulation of CD49d, which together with the beta1 chain constitutes VLA-4 integrin, may be responsible for the selective accumulation of T cells in the allergic asthmatic lung.

Expression of interleukin-5 and granulocyte-macrophage colony-stimulating factor in aspirin-sensitive and non-aspirin-sensitive asthmatic airways

Increased numbers of eosinophils and mast cells in the bronchial mucosa are characteristic features in subjects with aspirin-sensitive asthma. Interleukin-5 (IL-5) and granulocyte-macrophage colony-stimulating factor (GM-CSF) are involved in the activation, maturation, and perpetuation of survival of eosinophils. Immunohistochemical techniques were therefore used to study the expression of IL-5 and GM-CSF on frozen bronchial biopsies from 13 aspirin-sensitive asthmatic (ASA) and 8 non-ASA (NASA) subjects. Aspirin sensitivity was diagnosed by lysine-aspirin inhalation provocation. ASA airways demonstrated a significant 2-fold increase in the total number of submucosal inflammatory cells expressing IL-5 (p = 0.03) and approximate 4- and 2-fold increases in the numbers of mast cells expressing IL-5 and GM-CSF (p = 0.02 and p = 0.04, respectively). There was also a 4-fold increase in the number of eosinophils expressing IL-5 (p = 0.004). These results suggest a central role for the mast cell and eosinophil in regulation of the inflammatory cell infiltrate of ASA airways by secretion of the hemopoietic cytokines IL-5 and GM-CSF.

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

BACKGROUND

Eosinophils selectively accumulate at sites of allergic inflammation. Their recruitment is dependent on both the expression and functional activity of cell adhesion molecules. How the functional activity of cell adhesion molecules on eosinophils is regulated is poorly understood.

OBJECTIVE

Our objective was to examine the functional activity of alpha 4 integrins on human eosinophils and its regulation by various agents.

METHODS

Function of alpha 4 integrins on human eosinophils was examined by testing adhesion to immobilized fibronection and vascular cell adhesion molecule-1 (VCAM-1) in the presence or absence of a monoclonal antibody (mAb) (8A2) that activates beta 1 integrin function.

RESULTS

Spontaneous eosinophil adhesion to VCAM-1 was enhanced by 8A2, but adhesion to fibronectin could only be detected in the presence of 8A2. Concentrations of 8A2 that were approximately 100-fold less than saturating induced maximal eosinophil adhesion. Adhesion to VCAM-1 in the presence of 8A2 was effectively inhibited by alpha 4 and beta 1 integrin mAbs: beta 7 mAb had partial inhibitory activity. Connecting segment-1 peptide and alpha 4 mAb blocked 8A2-dependent fibronectin binding: beta 1, beta 2, and beta 7 integrin mAbs had partial inhibitory activity. Eosinophils obtained from bronchoalveolar lavage fluids and blood eosinophils stimulated with IL-5, platelet-activating factor, or RANTES displayed increased beta 2 integrin-dependent, not alpha 4 integrin-dependent, attachment. Spontaneous adhesion of eosinophils to VCAM-1 was significantly reduced by the tyrosine kinase inhibitor tyrphostin B46 (inhibitory concentration of 50% approximately equal to 20 mumol/L); this effect was reversed by 8A2.

CONCLUSIONS

The functional activity of integrins on eosinophils can be positively and negatively regulated. Altered integrin avidity may influence eosinophil recruitment in vivo.

Antibody to VLA-4, but not to L-selectin, protects neuronal M2 muscarinic receptors in antigen-challenged guinea pig airways

Antigen challenge of sensitized guinea pigs decreases the function of inhibitory M2 muscarinic autoreceptors on parasympathetic nerves in the lung, potentiating vagally induced bronchoconstriction. Loss of M2 receptor function is associated with the accumulation of eosinophils around airway nerves. To determine whether recruitment of eosinophils via expression of VLA-4 and L-selectin is critical for loss of M2 receptor function, guinea pigs were pretreated with monoclonal antibodies to VLA-4 (HP1/2) or L-selectin (LAM1-116). Guinea pigs were sensitized and challenged with ovalbumin, and M2 receptor function was tested. In controls, blockade of neuronal M2 muscarinic receptors by gallamine potentiated vagally induced bronchoconstriction, while in challenged animals this effect was markedly reduced, confirming M2 receptor dysfunction. Pretreatment with HP1/2, but not with LAM1-116, protected M2 receptor function in the antigen-challenged animals. HP1/2 also inhibited the development of hyperresponsiveness, and selectively inhibited accumulation of eosinophils in the lungs as measured by lavage and histology. Thus, inhibition of eosinophil influx into the lungs protects the function of M2 muscarinic receptors, and in so doing, prevents hyperresponsiveness in antigen-challenged guinea pigs.

Integrin alpha 4 beta 7 mediates human eosinophil interaction with MAdCAM-1, VCAM-1 and fibronectin

We have investigated the contribution of integrin alpha 4 beta 7 to human peripheral blood eosinophil adhesive interactions. Immunofluorescence and flow cytometry demonstrated constitutive expression of alpha 4 beta 7 by eosinophils. Expression of alpha 4 beta 7 or alpha 4 beta 7 was not enhanced by eosinophil activation with platelet-activating factor (PAF). Expression of alpha 4 beta 7 was confirmed by immuno-precipitation of 125I-labeled lysates analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE). Approximately 20% of unstimulated eosinophils were adherent to L1-2 cells transfected with vascular cell adhesion molecule-1 (VCAM-1) cDNA, while very few resting eosinophils adhered to mouse mucosal adressin cell adhesion molecule-1 (MAdCAM-1) transfectants. Binding of unstimulated eosinophils to VCAM-1 transfectant was inhibited by HPI 2 (an antibody that blocks both alpha 4 beta 1 and alpha 4 beta 7 functions), but not Act-1, and alpha 4 beta 1 monoclonal antibody (mAb). PAF stimulation resulted in increased binding of eosinophils to MAdCAM-1 transfectants, which was inhibited by both HPI 2 and Act-1. In contrast, PAF did not enhance binding to VCAM 1 transfectants, although binding of PAE-stimulated eosinophils to VCAM-1 could be partially inhibited by Act-1. Stimulation of eosinophils with the beta 7-activating mAb TS2 16 resulted in enhanced binding of eosinophils to both VCAM-1 and MAdCAM-1 transfectants. The increased binding was largely alpha 4 beta 7-dependent. Unstimulated eosinophils bound to soluble recombinant human (rh) VCAM-1 and fibronectin (Fn), coated on 96-well plates in dose-dependent manner. Binding was inhibited by HPI-2 and 4b4, an anti-beta 1 mAb, but not by Act-1. TS2 16 treatment increased adherent cell numbers and this enhanced binding was inhibited by Act-1. We have therefore confirmed that alpha 4 beta 7 is functionally active on unstimulated eosinophils. In contrast, PAF-induced enhancement of eosinophils binding to VCAM-1 or MAdCAM-1 was alpha 4 beta 7-dependent. In addition treatment with TS2 16 resulted in a alpha 4 beta 7-dependent enhancement of eosinophil binding to VCAM-1, MAdCAM-1 and Fn. We therefore hypothesize that alpha 4 beta 7 may have an important role in eosinophil localization in diseases such as asthma and inflammatory bowel disease.