Selective induction of intercellular adhesion molecule-1 by interferon-gamma in human airway epithelial cells

LasR-deficient Pseudomonas aeruginosa variants increase airway epithelial mICAM-1 expression and enhance neutrophilic lung inflammation

Pseudomonas aeruginosa causes chronic airway infections, a major determinant of lung inflammation and damage in cystic fibrosis (CF). Loss-of-function lasR mutants commonly arise during chronic CF infections, are associated with accelerated lung function decline in CF patients and induce exaggerated neutrophilic inflammation in model systems. In this study, we investigated how lasR mutants modulate airway epithelial membrane bound ICAM-1 (mICAM-1), a surface adhesion molecule, and determined its impact on neutrophilic inflammation in vitro and in vivo. We demonstrated that LasR-deficient strains induce increased mICAM-1 levels in airway epithelial cells compared to wild-type strains, an effect attributable to the loss of mICAM-1 degradation by LasR-regulated proteases and associated with enhanced neutrophil adhesion. In a subacute airway infection model, we also observed that lasR mutant-infected mice displayed greater airway epithelial ICAM-1 expression and increased neutrophilic pulmonary inflammation. Our findings provide new insights into the intricate interplay between lasR mutants, LasR-regulated proteases and airway epithelial ICAM-1 expression, and reveal a new mechanism involved in the exaggerated inflammatory response induced by lasR mutants.

The impact of 17β-estradiol and progesterone therapy on peripheral blood mononuclear cells of asthmatic patients

There is a significant fluctuation in clinical symptoms of asthmatic females during their life course, suggesting that the reproductive status and the level of sex hormones may affect the development of asthma and its exacerbation. In this study, we aimed to assess the biological effects of 17β-estradiol (E2) and progesterone (P4), alone or in combination form, on the transcription factors and production of cytokines in peripheral blood mononuclear cells (PBMCs). PBMCs of the mild-to-moderate asthmatic patients and healthy controls (HCs) were treated with equivalent serum levels of E2 or P4 maintained during hormone replacement therapy (HRT). The expression levels of T-bet, GATA-3, RORγt, PU.1, and Foxp3 were assessed by quantitative PCR. We also measured the concentration of IL-4, IL-9, IL-10, IFN-γ, and TGF-β in cell culture supernatants using ELISA. IL-4 production and GATA-3 expression levels slightly increased when asthmatic PBMCs were treated with E2 (p < 0.01), P4 (p < 0.01), or E2 + P4 (p < 0.001) compared to the untreated cells. IL-9 secretion (p < 0.001) and PU.1 gene expression levels (p < 0.05) were slightly higher in asthmatic patients' PBMCs before treatment but hormone therapy did not affect the level of them. Although the untreated asthmatic PBMCs produced a lower amount of IFN-γ compared to HCs (p < 0.01), hormone treatment did not affect the levels of IFN-γ secretion in patient groups. Moreover, we did not observe any significant changes in IL-10 and TGF-β secretion in the supernatant of hormone treated cells. We found that the common applied HRT may faintly increase GATA-3 expression and IL-4 production levels in PBMCs of asthmatic patients and can slightly increase asthma severity.

Acute Tubular Injury is Associated With Severe Traumatic Brain Injury: in Vitro Study on Human Tubular Epithelial Cells

Acute kidney injury following traumatic brain injury is associated with poor outcome. We investigated in vitro the effects of plasma of brain injured patients with acute tubular kidney injury on kidney tubular epithelial cell function. we performed a prospective observational clinical study in ICU in a trauma centre of the University hospital in Italy including twenty-three ICU patients with traumatic brain injury consecutively enrolled. Demographic data were recorded on admission: age 39 ± 19, Glasgow Coma Score 5 (3–8). Neutrophil Gelatinase-Associated Lipocalin and inflammatory mediators were measured in plasma on admission and after 24, 48 and 72 hours; urine were collected for immunoelectrophoresis having healthy volunteers as controls. Human renal proximal tubular epithelial cells were stimulated with patients or controls plasma. Adhesion of freshly isolated human neutrophils and trans-epithelial electrical resistance were assessed; cell viability (XTT assay), apoptosis (TUNEL staining), Neutrophil Gelatinase-Associated Lipocalin and Megalin expression (quantitative real-time PCR) were measured. All patients with normal serum creatinine showed increased plasmatic Neutrophil Gelatinase-Associated Lipocalin and increased urinary Retinol Binding Protein and α1-microglobulin. Neutrophil Gelatinase-Associated Lipocalin was significantly correlated with both inflammatory mediators and markers of tubular damage. Patient’ plasma incubated with tubular cells significantly increased adhesion of neutrophils, reduced trans-epithelial electrical resistance, exerted a cytotoxic effect and triggered apoptosis and down-regulated the endocytic receptor Megalin compared to control. Plasma of brain injured patients with increased markers of subclinical acute kidney induced a pro-inflammatory phenotype, cellular dysfunction and apoptotic death in tubular epithelial cells.

Neutrophil-Epithelial Interactions: A Double-Edged Sword

In recent years, it has become clear that innate immune cells termed neutrophils act as double-edged swords by playing essential roles in clearing infection but also causing tissue damage, yet being critical for wound healing. Neutrophil recruitment to sites of injured tissue or infection has been well studied, and many of the molecular events that regulate passage of leukocytes out of the microcirculation are now understood. However, after exiting the circulation, the molecular details that regulate neutrophil passage to end targets, such mucosal surfaces, are just beginning to be appreciated. Given that migration of neutrophils across mucosal epithelia is associated with disease symptoms and disruption of critical barrier function in disorders such as inflammatory bowel disease, there has been long-standing interest in understanding the molecular basis and functional consequences of neutrophil-epithelial interactions. It is a great honor that my work was recognized by the Rous-Whipple Award this past year, giving me the opportunity to summarize what we have learned during the past few decades about leukocyte interactions with epithelial cells.

Epithelial adhesion molecules and the regulation of intestinal homeostasis during neutrophil transepithelial migration

Epithelial adhesion molecules play essential roles in regulating cellular function and maintaining mucosal tissue homeostasis. Some form epithelial junctional complexes to provide structural support for epithelial monolayers and act as a selectively permeable barrier separating luminal contents from the surrounding tissue. Others serve as docking structures for invading viruses and bacteria, while also regulating the immune response. They can either obstruct or serve as footholds for the immune cells recruited to mucosal surfaces. Currently, it is well appreciated that adhesion molecules collectively serve as environmental cue sensors and trigger signaling events to regulate epithelial function through their association with the cell cytoskeleton and various intracellular adapter proteins. Immune cells, particularly neutrophils (PMN) during transepithelial migration (TEM), can modulate adhesion molecule expression, conformation, and distribution, significantly impacting epithelial function and tissue homeostasis. This review discusses the roles of key intestinal epithelial adhesion molecules in regulating PMN trafficking and outlines the potential consequences on epithelial function.

Adhesion of pancreatic cancer cells in a liver-microvasculature mimicking coculture correlates with their propensity to form liver-specific metastasis in vivo

Organ-specific characteristic of endothelial cells (ECs) is crucial for specific adhesion of cancer cells to ECs, which is a key factor in the formation of organ-specific metastasis. In this study, we developed a coculture of TMNK-1 (immortalized liver sinusoidal ECs) with 10T1/2 (resembling hepatic stellate cells) to augment organ-specific characteristic of TMNK-1 and investigated adhesion of two pancreatic cancer cells (MIA-PaCa-2 and BxPC-3) in the culture. MIA-PaCa-2 and BxPC-3 adhesion in TMNK-1+10T1/ 2|coating culture (TMNK-1 monolayer over 10T1/2 layer on collagen coated surface) were similar. However, in TMNK-1+10T1/ 2|gel (coculture on collagen gel surface), MIA-PaCa-2 adhesion was significantly higher than BxPC-3, which was congruent with the reported higher propensity of MIA-PaCa-2 than BxPC-3 to form liver metastasis in vivo. Notably, as compared to BxPC-3, MIA-PaCa-2 adhesion was lower and similar in TMNK-1 only culture on the collagen coated and gel surfaces, respectively. Investigation of the adhesion in the representative human umbilical vein ECs (HUVECs) cultures and upon blocking of surface molecules of ECs revealed that MIA-PaCa-2 adhesion was strongly dependent on the organ-specific upregulated characteristics of TMNK-1 in TMNK-1+10T1/ 2|gel culture. Therefore, the developed coculture would be a potential assay for screening novel drugs to inhibit the liver-microvasculature specific adhesion of cancer cells.

Inositol-requiring enzyme 1 inhibits respiratory syncytial virus replication

Despite being a major health problem, respiratory syncytial virus (RSV) infections remain without specific therapy. Identification of novel host cellular responses that play a role in the pathogenesis of RSV infection is needed for therapeutic development. The endoplasmic reticulum (ER) stress response is an evolutionarily conserved cellular signaling cascade that has been implicated in multiple biological phenomena, including the pathogenesis of some viral infections. In this study, we investigate the role of the ER stress response in RSV infection using an in vitro A549 cell culture model. We found that RSV infection induces a non-canonical ER stress response with preferential activation of the inositol-requiring enzyme 1 (IRE1) and activated transcription factor 6 (ATF6) pathways with no concomitant significant activation of the protein kinase R-like ER kinase (PERK) pathway. Furthermore, we discovered that IRE1 has an inhibitory effect on RSV replication. Our data characterize, for the first time, the nature of the ER stress response in the setting of RSV infection and identify the IRE1 stress pathway as a novel cellular anti-RSV defense mechanism.

NOD-like receptors mediated activation of eosinophils interacting with bronchial epithelial cells: a link between innate immunity and allergic asthma

Key intracytosolic pattern recognition receptors of innate immunity against bacterial infections are nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs). We elucidated the NOD1 and NOD2-mediated activation of human eosinophils, the principal effector cells for allergic inflammation, upon interacting with human bronchial epithelial BEAS-2B cells in allergic asthma. Eosinophils constitutively expressed NOD1,2 but exhibited nonsignificant responses to release chemokines upon the stimulation by NOD1 ligand γ-D-glutamyl-meso-diaminopimelic acid (iE-DAP) and NOD2 ligand muramyl dipeptide (MDP). However, iE-DAP and MDP could significantly upregulate cell surface expression of CD18 and intercellular adhesion molecule (ICAM)-1 on eosinophils and ICAM-1 on BEAS-2B cells, as well as induce chemokines CCL2 and CXCL8 release in the coculture system (all P<0.05). Both eosinophils and BEAS-2B cells were the main source for CXCL8 and CCL2 release in the coculture system upon iE-DAP or MDP stimulation. Direct interaction between eosinophils and BEAS-2B cells is responsible for CCL2 release, and soluble mediators are implicated in CXCL8 release. ERK and NF-κB play regulatory roles for the expression of adhesion molecules and chemokines in coculture. Treatment with NOD1,2 ligand could induce the subepithelial fibrosis and significantly enhance the serum concentration of total IgE, chemokine CCL5 for eosinophils and T helper type 2 (Th2) cells and asthma Th2 cytokine IL-13 in bronchoalveolar lavage fluid of ovalbumin-sensitized allergic asthmatic mice (all P<0.05). This study provides further evidence of bacterial infection-mediated activation of NOD1,2 in triggering allergic asthma via the activation of eosinophils interacting with bronchial epithelial cells at inflammatory airway.

Influenza A viral replication is blocked by inhibition of the inositol-requiring enzyme 1 (IRE1) stress pathway

Known therapies for influenza A virus infection are complicated by the frequent emergence of resistance. A therapeutic strategy that may escape viral resistance is targeting host cellular mechanisms involved in viral replication and pathogenesis. The endoplasmic reticulum (ER) stress response, also known as the unfolded protein response (UPR), is a primitive, evolutionary conserved molecular signaling cascade that has been implicated in multiple biological phenomena including innate immunity and the pathogenesis of certain viral infections. We investigated the effect of influenza A viral infection on ER stress pathways in lung epithelial cells. Influenza A virus induced ER stress in a pathway-specific manner. We showed that the virus activates the IRE1 pathway with little or no concomitant activation of the PERK and the ATF6 pathways. When we examined the effects of modulating the ER stress response on the virus, we found that the molecular chaperone tauroursodeoxycholic acid (TUDCA) significantly inhibits influenza A viral replication. In addition, a specific inhibitor of the IRE1 pathway also blocked viral replication. Our findings constitute the first evidence that ER stress plays a role in the pathogenesis of influenza A viral infection. Decreasing viral replication by modulating the host ER stress response is a novel strategy that has important therapeutic implications.

Reduced inflammation and altered innate response in neonates during paramyxoviral infection

Background

Human infants are frequently hospitalized due to infection with the paramyxovirus respiratory syncytial virus (RSV). However, very little is known about the neonatal response to paramyxoviral infection. Here, a neonatal model of paramyxoviral infection is developed using the mouse pathogen Sendai virus (SeV).

Results

Adult mice infected with SeV developed a predominantly neutrophilic inflammatory cell influx and a concomitant reduction in lung function, as determined by oxygen saturation. In contrast, neonates with SeV had significantly reduced inflammation and normal lung function. Surprisingly, infected neonates had similar viral loads as adult mice. A reduced neutrophil influx in the neonates may be due in part to reduced expression of both CXCL2 and intracellular adhesion molecule-1 (ICAM-1). Expression of IFN-γ and TNF-α increased in a dose-dependent manner in adult lungs, but neonates did not increase expression of either of these cytokines, even at the highest doses. Importantly, the expression of the RIG-I-like receptors (RLRs) was delayed in the neonatal mice, which might have contributed to their reduced inflammation and differential cytokine expression.

Conclusions

Neonatal mice developed similar SeV titers and cleared the virus with similar efficiency despite developing a dramatically lower degree of pulmonary inflammation compared to adults. This suggests that inflammation in the lung may not be required to control viral replication. Future studies will be needed to determine any effect the reduced inflammation may have on the development of a protective memory response in neonates.

Host epithelial-viral interactions as cause and cure for asthma

Research on the pathogenesis of asthma has concentrated on initial stimuli, genetic susceptibilities, adaptive immune responses, and end-organ alterations (particularly in airway mucous cells and smooth muscle) as critical steps leading to disease. Recent evidence indicates that the innate immune cell response to respiratory viruses also contributes to the development of inflammatory airway disease. We further develop this concept by raising the issue that the interaction between host airway epithelial cells and respiratory viruses is another aspect of innate immunity that is also a critical determinant of asthma. We also introduce a rationale for how antiviral performance at the epithelial cell level might be improved to prevent acute infectious illness and chronic inflammatory disease caused by respiratory viruses.

The other T helper cells in asthma pathogenesis

The complex phenotype of allergic bronchial asthma involves a variable degree of bronchoobstruction, increased mucus production, and airway remodeling. So far it is suggested that it arises from multiple interactions of infiltrating and structural cells in the context of chronic airway inflammation that is orchestrated by T helper 2 (TH2) cells. By secreting a plethora of typical mediators such as interleukin (IL) 4, IL-5, and IL-13, these cells hold a key position in asthma pathogenesis. However, therapeutic approaches targeting these TH2-type mediators failed to improve asthma symptoms and impressively showed that asthma pathogenesis cannot be reduced by TH2 cell functions. Recently, other T helper cells, that is, TH9 and TH17 cells, have been identified and these cells also contribute to asthma pathogenesis, the processes leading to formation or aggravation of asthma. Furthermore, TH25 cells, TH3 cells, and regulatory T cells have also been implicated in asthma pathogenesis. This paper aims at summarizing recent insights about these new T helper cells in asthma pathogenesis.

Inhibition of IFN-gamma-dependent antiviral airway epithelial defense by cigarette smoke

BACKGROUND

Although individuals exposed to cigarette smoke are more susceptible to respiratory infection, the effects of cigarette smoke on lung defense are incompletely understood. Because airway epithelial cell responses to type II interferon (IFN) are critical in regulation of defense against many respiratory viral infections, we hypothesized that cigarette smoke has inhibitory effects on IFN-gamma-dependent antiviral mechanisms in epithelial cells in the airway.

METHODS

Primary human tracheobronchial epithelial cells were first treated with cigarette smoke extract (CSE) followed by exposure to both CSE and IFN-gamma. Epithelial cell cytotoxicity and IFN-gamma-induced signaling, gene expression, and antiviral effects against respiratory syncytial virus (RSV) were tested without and with CSE exposure.

RESULTS

CSE inhibited IFN-gamma-dependent gene expression in airway epithelial cells, and these effects were not due to cell loss or cytotoxicity. CSE markedly inhibited IFN-gamma-induced Stat1 phosphorylation, indicating that CSE altered type II interferon signal transduction and providing a mechanism for CSE effects. A period of CSE exposure combined with an interval of epithelial cell exposure to both CSE and IFN-gamma was required to inhibit IFN-gamma-induced cell signaling. CSE also decreased the inhibitory effect of IFN-gamma on RSV mRNA and protein expression, confirming effects on viral infection. CSE effects on IFN-gamma-induced Stat1 activation, antiviral protein expression, and inhibition of RSV infection were decreased by glutathione augmentation of epithelial cells using N-acetylcysteine or glutathione monoethyl ester, providing one strategy to alter cigarette smoke effects.

CONCLUSIONS

The results indicate that CSE inhibits the antiviral effects of IFN-gamma, thereby presenting one explanation for increased susceptibility to respiratory viral infection in individuals exposed to cigarette smoke.

Fibrinogen binding to ICAM-1 promotes EGFR-dependent mucin production in human airway epithelial cells

Mucous hypersecretion is a serious feature of chronic airway diseases such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. Although mucins are produced via activation of an EGF receptor (EGFR) signaling cascade, the mechanisms leading to exaggerated mucin production in mucous hypersecretory diseases are unknown. Because expression of ICAM-1 and of the ICAM-1 ligand fibrinogen is increased in the airways of subjects with mucous hypersecretory diseases, we hypothesized that fibrinogen binding to ICAM-1 could increase EGFR-dependent mucin production in human airway (NCI-H292) epithelial cells. Consistent with this hypothesis, we found that an ICAM-1 neutralizing antibody and an ICAM-1(8-22) peptide that binds fibrinogen decreased mucin production induced by the EGFR ligand transforming growth factor (TGF)-alpha dose-dependently. Exogenous fibrinogen and a fibrinogen(117-133) peptide that binds ICAM-1 rescued mucin production in cells treated with the ICAM-1(8-22) peptide. Surprisingly, the ICAM-1(8-22) peptide increased EGFR phosphotyrosine and phospho-ERK1/2 in cells treated with TGF-alpha. The ICAM-1(8-22) peptide-induced increases in EGFR phosphotyrosine and phospho-ERK1/2 were prevented by exogenous fibrinogen, by the fibrinogen(117-133) peptide, and by selective inhibitors of phospholipase C (PLC), protein kinase C (PKC)-alpha/beta, and metalloproteases. These results suggest that fibrinogen binding to ICAM-1 promotes mucin production by decreasing TGF-alpha-induced EGFR and ERK1/2 activation and that the fibrinogen-ICAM-1-dependent decrease in EGFR and ERK1/2 activation occurs via inhibition of an early positive feedback pathway involving PLC- and PKC-alpha/beta-dependent metalloprotease activation and subsequent metalloprotease-dependent EGFR reactivation.

Transepithelial migration of neutrophils: mechanisms and implications for acute lung injury

The primary function of neutrophils in host defense is to contain and eradicate invading microbial pathogens. This is achieved through a series of swift and highly coordinated responses culminating in ingestion (phagocytosis) and killing of invading microbes. While these tasks are usually performed without injury to host tissues, in pathologic circumstances such as sepsis, potent antimicrobial compounds can be released extracellularly, inducing a spectrum of responses in host cells ranging from activation to injury and death. In the lung, such inflammatory damage is believed to contribute to the pathogenesis of diverse lung diseases, including acute lung injury and the acute respiratory distress syndrome, chronic obstructive lung disease, and cystic fibrosis. In these disorders, epithelial cells are targets of leukocyte-derived antimicrobial products, including proteinases and oxidants. Herein, we review the mechanisms involved in the physiologic process of neutrophil transepithelial migration, including the role of specific adhesion molecules on the leukocyte and epithelial cells. We examine the responses of the epithelial cells to the itinerant leukocytes and their cytotoxic products and the consequences of this for lung injury and repair. This paradigm has important clinical implications because of the potential for selective blockade of these pathways to prevent or attenuate lung injury.

Tryptase activates calcium-independent phospholipase A2 and releases PGE2 in airway epithelial cells

Human small airway epithelial cells (HSAEC) form the boundary between the external environmental allergens and the internal lung milieu. Mast cells are present in human lung tissue interspersed within the pulmonary epithelium and can secrete a host of pre- and newly formed mediators from their granules, which may propagate small airway inflammation. In this study, tryptase stimulation of HSAEC increased membrane-associated, calcium-independent phospholipase A(2)gamma (iPLA(2)gamma) activity, resulting in increased arachidonic acid and PGE(2) release. These responses were inhibited by pretreating HSAEC with the iPLA(2)-selective inhibitor bromoenol lactone. The tryptase-stimulated PGE(2) production was inhibited by treating HSAEC with the cyclooxygenase (COX)-1-selective inhibitor SC-560 and the nonselective COX inhibitor aspirin but not by the COX-2-selective inhibitor CAY10404, indicating that the early release of arachidonic acid is metabolized by constitutive COX-1 to form PGE(2) in tryptase-stimulated HSAEC. Additionally, platelet-activating factor production and neutrophil adherence to tryptase-stimulated HSAEC was also increased. This complex response can set up a cascade of inflammatory mediator production in small airways. We speculate that selective inhibition of iPLA(2)gamma-mediated phospholipid hydrolysis may prove beneficial in inflammatory airway diseases.

Regulation of bacteria-induced intercellular adhesion molecule-1 by CCAAT/enhancer binding proteins

Direct interaction between bacteria and epithelial cells may initiate or amplify the airway response through induction of epithelial defense gene expression by nuclear factor-kappaB (NF-kappaB). However, multiple signaling pathways modify NF-kappaB effects to modulate gene expression. In this study, the effects of CCAAT/enhancer binding protein (C/EBP) family members on induction of the leukocyte adhesion glycoprotein intercellular adhesion molecule-1 (ICAM-1) was examined in primary cultures of human tracheobronchial epithelial cells incubated with nontypeable Haemophilus influenzae. Increased ICAM-1 gene transcription in response to H. influenzae required gene sequences located at -200 to -135 in the 5'-flanking region that contain a C/EBP-binding sequence immediately upstream of the NF-kappaB enhancer site. Constitutive C/EBPbeta was found to have an important role in epithelial cell ICAM-1 regulation, while the adjacent NF-kappaB sequence binds the RelA/p65 and NF-kappaB1/p50 members of the NF-kappaB family to induce ICAM-1 expression in response to H. influenzae. The expression of C/EBP proteins is not regulated by p38 mitogen-activated protein kinase activation, but p38 affects gene transcription by increasing the binding of TATA-binding protein to TATA-box-containing gene sequences. Epithelial cell ICAM-1 expression in response to H. influenzae was decreased by expressing dominant-negative protein or RNA interference against C/EBPbeta, confirming its role in ICAM-1 regulation. Although airway epithelial cells express multiple constitutive and inducible C/EBP family members that bind C/EBP sequences, the results indicate that C/EBPbeta plays a central role in modulation of NF-kappaB-dependent defense gene expression in human airway epithelial cells after exposure to H. influenzae.

IFN-gamma regulation of ICAM-1 receptors in bronchial epithelial cells: soluble ICAM-1 release inhibits human rhinovirus infection

Background

Intercellular adhesion molecule-1 (ICAM-1) is a critical target-docking molecule on epithelial cells for 90% of human rhinovirus (HRV) serotypes. Two forms of ICAM-1 exist, membranous (mICAM-1) and soluble (sICAM-1), both expressed by bronchial epithelial cells. Interferon-gamma (IFN-γ), a crucial Th-1 immuno-regulatory mediator, can modulate mICAM-1 expression; however its simultaneous effects on mICAM-1: sICAM-1 levels and their consequent outcome on cell infectivity have not been previously explored.

Methods

Primary normal human bronchial epithelial cells were pre-stimulated with IFN-γ (1 ng/ml for 24 h) and subsequently inoculated with HRV-14 or HRV-1b (TCID₅₀ 10 ^2.5). Epithelial surface ICAM-1 expression and soluble ICAM-1 release were measured at the protein and gene level by immunofluorescence and ELISA respectively; mRNA levels were semi-quantified using RT-PCR. Molecular mechanisms regulating ICAM-1 isoform expression and effects on epithelial cell infectivity were explored.

Results

In IFN-γ-biased cells infected with HRV-14, but not HRV-1b, mICAM-1 expression is down-regulated, with simultaneous induction of sICAM-1 release. This differential effect on HRV-14 receptor isoforms appears to be related to a combination of decreased IFN-γ-induced JAK-STAT signalling and proteolytic receptor cleavage of the membranous form in IFN-γ-biased HRV-14 infected cells. The observed changes in relative mICAM-1: sICAM-1 expression levels are associated with reduced HRV-14 viral titres.

Conclusion

These findings support the hypothesis that in epithelial cells conditioned to IFN-γ and subsequently exposed to HRV-14 infection, differential modulation in the ratio of ICAM-1 receptors prevails in favour of an anti-viral milieu, appearing to limit further target cell viral attachment and propagation.

Cysteinyl leukotriene-1 receptor activation in a human bronchial epithelial cell line leads to signal transducer and activator of transcription 1-mediated eosinophil adhesion

We studied the effect of leukotriene D(4) (LTD(4)) on a human bronchial epithelial cell line (16HBE) overexpressing the cysteinyl leukotriene (CysLT) (1) receptor (HBECysLT(1)R), looking at the associated signal transduction mechanisms as well as at effects on inflammatory cell adhesion. The results obtained showed that LTD(4) increases the phosphorylation of extracellular signal-regulated protein kinase (ERK) 1/2 and of the signal transducer and activator of transcription 1 (STAT-1) in serine 727 (STAT-1Ser727), resulting in increased eosinophil adhesion to HBECysLT(1)R, associated with enhanced surface expression of intercellular adhesion molecule (ICAM) 1. Pretreatment with a CysLT(1)R-selective antagonist or with a selective inhibitor of protein kinase C (PKC) or with a selective inhibitor of the mitogen-activated protein kinase kinase (MEK) successfully suppressed both LTD(4)-induced STAT-1Ser727 phosphorylation and the associated increase in eosinophil adhesion. The use of the MEK inhibitor and of the selective CysLT(1)R antagonist in electrophoretic mobility shift assay experiments showed that LTD(4) promotes the nuclear translocation of STAT-1 through the activation of ERK1/2 pathway. The key role of STAT-1 in leukotriene D(4) transduction signaling was confirmed by RNA interference experiments, where silencing of STAT-1 expression abolished the effect of leukotriene D(4) on eosinophil adhesion. In conclusion, for the first time, we provide evidence of the involvement of STAT-1 in the signal transduction mechanism of the CysLT(1) receptor; phosphorylation of STAT-1, through PKC and ERK1/2 activation, causes enhanced ICAM-1 surface expression and eosinophil adhesion. Effective CysLT(1)R antagonism may therefore contribute to the control of the chronic inflammatory condition that characterizes human airways in asthma.

Alpha-4/beta-1 and alpha-L/beta-2 integrins mediate cytokine induced lung leukocyte-epithelial adhesion and injury

BACKGROUND AND PURPOSE

Injury to the alveolar epithelium is a critical feature of acute lung injury (ALI). Using a cytokine model of ALI we demonstrated previously that newly recruited mononuclear phagocytes (MNP) contributed to lung inflammation and injury. We hypothesized that cytokines delivered into the alveolar airspace would have multiple effects on the lung that may contribute to lung injury.

EXPERIMENTAL APPROACH

Intratracheal cytokine insufflation and leukocyte adoptive transfer in vivo were combined with in vitro analyses of lung epithelial cell-MNP adhesion and injury. Lung inflammatory injury was assessed by histology, leukocyte infiltration, and release of LDH and RAGE.

KEY RESULTS

Cytokine insufflation was associated with apparent MNP-epithelial adhesion, up-regulation of alveolar ICAM-1 and VCAM-1, and the release of LDH and RAGE into the bronchoalveolar lavage. Insufflation of small molecule integrin antagonists suppressed adhesion of MNP and modulated release of LDH and RAGE. Adoptive transfer of MNP purified from cytokine insufflated lungs into leukopenic rats demonstrated the requirement of MNP for release of LDH that was not induced by cytokine alone. Corroboration that disrupting the ICAM/LFA1 interaction or the VCAM/VLA4 interaction blocked MNP-epithelial cell interaction and injury was obtained in vitro using both blocking monoclonal antibodies and the small molecule integrin antagonists, BIO5192 and XVA143.

CONCLUSIONS AND IMPLICATIONS

MNP recruited following cytokine insufflation contributed to lung injury. Further, integrin antagonists reduced alveolar epithelial cell injury induced during lung inflammation. Intratracheal delivery of small molecule antagonsists of leukocyte-epithelial adhesion that prevent lung injury may have significant clinical utility.

Inhibition of Jak1-dependent signal transduction in airway epithelial cells infected with adenovirus

Adenoviral evolution has generated mechanisms to resist host cell defense systems, but the biochemical basis for evasion of multiple antiviral pathways in the airway by adenoviruses is incompletely understood. We hypothesized that adenoviruses modulate airway epithelial responses to type I interferons by altering the levels and activation of specific Janus family kinase-signal transducer and activator of transcription (JAK-STAT) signaling components. In this study, specific effects of adenovirus type 5 (AdV) on selected JAK-STAT signal transduction pathways were identified in human tracheobronchial epithelial cells, with focus on type I interferon-dependent signaling and gene expression. We found that wild-type AdV infection inhibited IFN-alpha-induced expression of antiviral proteins in epithelial cells by blocking phosphorylation of the Stat1 and Stat2 transcription factors that are required for activation of type I interferon-dependent genes. These effects correlated with AdV-induced down-regulation of expression of the receptor-associated tyrosine kinase Jak1 through a decrease in Jak1 mRNA levels. Phosphorylation of Stat3 in response to IL-6 and oncostatin M was also lost in AdV-infected cells, indicating loss of epithelial cell responses to other cytokines that depend on Jak1. In contrast, IL-4- and IL-13-dependent phosphorylation of Stat6 was not affected during AdV infection, indicating that the virus modulates specific signaling pathways, as these Stat6-activating pathways can function independent of Jak1. Taken together, the results indicate that AdV down-regulates host epithelial cell Jak1 to assure inhibition of the antiviral effects of multiple mediators to subvert airway defense responses and establish a productive infection.

Defining and adjusting divergent host responses to viral infection

Our laboratory focuses on the signal-transduction basis for mucosal immunity, inflammation, and remodeling, especially in relation to respiratory viral infection. Our approach aims to answer two major questions: (1) What are the mechanisms that control common viral infections? and (2) How can these transient infections cause long-term diseases, such as asthma? Our studies show that antiviral defense depends critically on a specialized network of mucosal epithelial cells and macrophages. When this network is compromised, the host is highly susceptible to infection, but when it is engineered to be broadly hyperresponsive to interferon, the host is markedly resistant to otherwise lethal viral infections. Similar but less effective hyperresponsiveness appears in asthma, suggesting that evolving attempts to improve antiviral defense may instead cause inflammatory disease. Indeed, in susceptible genetic backgrounds, respiratory viruses can also cause a hit-and-run phenomenon that is manifest by the development of a permanent asthmatic phenotype long after the infection has been cleared. This complex phenotype can be segregated into individual traits using pharmacologic, immunologic, and genetic strategies to achieve more precise definition of just how viruses can reprogram host behavior. Evidence of reprogramming is manifest by persistent abnormalities in epithelial cell survival and macrophage activation that when corrected can prevent the development of disease phenotypes. Our results led us to pursue the hypothesis that specific components of the innate immune system may manifest an aberrant antiviral response as a basis for chronic inflammatory diseases and that adjusting this response can improve short- and long-term outcomes after viral infection.

Acute and chronic airway responses to viral infection: implications for asthma and chronic obstructive pulmonary disease

Despite the high clinical impact of established and emerging respiratory viruses, some critical aspects of the host response to these pathogens still need to be defined. In that context, we aimed at two major issues: first, what are the innate immune mechanisms that control common respiratory viral infections; and second, whether these mechanisms also cause long-term airway disease. Using a mouse model of viral bronchiolitis, we found that antiviral defense depends at least in part on a network of mucosal epithelial cells and macrophages specially programmed for immune-response gene expression. When this network is compromised, the host is highly susceptible to infection, but network components can be engineered to provide increased resistance to infection. Similar alterations appear in asthma and chronic bronchitis/chronic obstructive pulmonary disease, suggesting that evolving attempts to improve antiviral defense may also lead to inflammatory airway disease. Indeed, in genetically susceptible mice, respiratory paramyxoviruses cause a "hit and run" phenomenon that is manifested by the development of a permanent airway disease phenotype long after the infection has cleared. The phenotype can be segregated into individual traits to achieve more precise definition of just how viruses reprogram host behavior. Identifying specific components of the mucosal immune system that manifest an aberrant antiviral response may thereby allow for adjusting this response to improve acute and chronic outcomes after viral infection.

Haemophilus influenzae from patients with chronic obstructive pulmonary disease exacerbation induce more inflammation than colonizers

RATIONALE

Airway infection with Haemophilus influenzae causes airway inflammation, and isolation of new strains of this bacteria is associated with increased risk of exacerbations in patients with chronic obstructive pulmonary disease (COPD).

OBJECTIVE

To determine whether strains of H. influenzae associated with exacerbations cause more inflammation than strains that colonize the airways of patients with COPD.

METHODS

Exacerbation strains of H. influenzae were isolated from patients during exacerbation of clinical symptoms with subsequent development of a homologous serum antibody response and were compared with colonization strains that were not associated with symptom worsening or an antibody response. Bacterial strains were compared using an in vivo mouse model of airway infection and in vitro cell culture model of bacterial adherence and defense gene and signaling pathway activation in primary human airway epithelial cells.

RESULTS

H. influenzae associated with exacerbations caused more airway neutrophil recruitment compared with colonization strains in the mouse model of airway bacterial infection. Furthermore, exacerbation strains adhered to epithelial cells in significantly higher numbers and induced more interleukin-8 release after interaction with airway epithelial cells. This effect was likely mediated by increased activation of the nuclear factor-kappaB and p38 mitogen-activated protein kinase signaling pathways.

CONCLUSIONS

The results indicate that H. influenzae strains isolated from patients during COPD exacerbations often induce more airway inflammation and likely have differences in virulence compared with colonizing strains. These findings support the concept that bacteria infecting the airway during COPD exacerbations mediate increased airway inflammation and contribute to decreased airway function.

Increased interleukin-4, interleukin-5, and interferon-gamma in airway CD4+ and CD8+ T cells in atopic asthma

Increased Th2 cytokine production in asthma is widely accepted, but excess production by asthmatic human airway CD4(+) T cells has not been demonstrated, nor has a relationship with disease severity. The importance of airway CD8(+) T cell type 1 and type 2 cytokine production in asthma is unknown. We investigated frequencies of IFN-gamma, interleukin (IL)-4 and IL-5 producing CD4(+) and CD8(+) blood and sputum T cells from normal subjects and subjects with asthma and compared between cell subsets, subject groups, and body compartments with and without in vitro stimulation and investigated relationships between cytokine production and asthma severity. Production of IL-4, IL-5, and IFN-gamma by unstimulated sputum CD4(+) and CD8(+) T cells was increased in subjects with asthma and related to disease severity, more for CD8(+) than for CD4(+) T cells. Frequencies of sputum CD8(+) T cells producing type 1 and type 2 cytokines were similar to those of CD4(+) T cells. In vitro stimulation polarized peripheral blood cytokine production toward IFN-gamma production, significantly more in subjects with asthma than in normal subjects. These data demonstrate increased type 1 and 2 cytokine production in CD4(+) and CD8(+) T cells in sputum and relate production to disease severity. Findings in blood did not reflect those in airways.

Involvement of p42/p44 MAPK, p38 MAPK, JNK, and NF-kappaB in IL-1beta-induced VCAM-1 expression in human tracheal smooth muscle cells

Interleukin-1beta (IL-1beta) has been shown to induce the expression of adhesion molecules on airway epithelial and smooth cells and contributes to inflammatory responses. Here, the roles of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappaB (NF-kappaB) pathways for IL-1beta-induced vascular cell adhesion molecule (VCAM)-1 expression were investigated in human tracheal smooth muscle cells (HTSMC). IL-1beta induced expression of VCAM-1 protein and mRNA in a time-dependent manner, which was significantly inhibited by inhibitors of MEK1/2 (U0126 and PD-98059), p38 (SB-202190), and c-Jun NH(2)-terminal kinase (JNK; SP-600125). Consistently, IL-1beta-stimulated phosphorylation of p42/p44 MAPK, p38, and JNK was attenuated by pretreatment with U0126, SB-202190, or SP-600125, respectively. IL-1beta-induced VCAM-1 expression was significantly blocked by the specific NF-kappaB inhibitors helenalin and pyrrolidine dithiocarbamate. As expected, IL-1beta-stimulated translocation of NF-kappaB into the nucleus and degradation of IkappaB-alpha were blocked by helenalin but not by U0126, SB-202190, or SP-600125. Moreover, the resultant enhancement of VCAM-1 expression increased the adhesion of polymorphonuclear cells to a monolayer of HTSMC, which was blocked by pretreatment with helenalin, U0126, SB-202190, or SP-600125 before IL-1beta exposure or by anti-VCAM-1 antibody. Together, these results suggest that in HTSMC, activation of p42/p44 MAPK, p38, JNK, and NF-kappaB pathways is essential for IL-1beta-induced VCAM-1 gene expression. These results provide new insight into the mechanisms of IL-1beta action that cytokines may promote inflammatory responses in airway disease.

Modulation of airway inflammation and bacterial clearance by epithelial cell ICAM-1

Many cell types in the airway express the adhesive glycoprotein for leukocytes intercellular adhesion molecule-1 (ICAM-1) constitutively and/or in response to inflammatory stimuli. In this study, we identified functions of ICAM-1 on airway epithelial cells in defense against infection with Haemophilus influenzae. Initial experiments using a mouse model of airway infection in which the bacterial inoculum was mixed with agar beads that localize inflammation in airways demonstrated that ICAM-1 expression was required for efficient clearance of H. influenzae. Airway epithelial cell ICAM-1 expression required few or no leukocytes, suggesting that epithelial cells could be activated directly by interaction with bacteria. Specific inhibition of ICAM-1 function on epithelial cells by orotracheal injection of blocking antibodies resulted in decreased leukocyte recruitment and H. influenzae clearance in the airway. Inhibition of endothelial cell ICAM-1 resulted in a similar decrease in leukocyte recruitment but did not affect bacterial clearance, indicating that epithelial cell ICAM-1 had an additional contribution to airway defense independent of effects on leukocyte migration. To assess this possibility, we used an in vitro model of neutrophil phagocytosis of bacteria and observed significantly greater engulfment of bacteria by neutrophils adherent to epithelial cells expressing ICAM-1 compared with nonadherent neutrophils. Furthermore, bacterial phagocytosis and killing by neutrophils after interaction with epithelial cells were decreased when a blocking antibody inhibited ICAM-1 function. The results indicate that epithelial cell ICAM-1 participates in neutrophil recruitment into the airway, but its most important role in clearance of H. influenzae may be assistance with neutrophil-dependent bacterial killing.

Specific Inhibition of Type I Interferon Signal Transduction by Respiratory Syncytial Virus

Respiratory viruses often express mechanisms to resist host antiviral systems, but the biochemical basis for evasion of interferon effects by respiratory syncytial virus (RSV) is poorly defined. In this study, we identified RSV effects on interferon (IFN)-dependent signal transduction and gene expression in human airway epithelial cells. Initial experiments demonstrated inhibition of antiviral gene expression induced by IFN-alpha and IFN-beta, but not IFN-gamma, in epithelial cells infected with RSV. Selective viral effects on type I IFN-dependent signaling were confirmed when we observed impaired type I, but not type II, IFN-induced activation of the transcription factor Stat1 in RSV-infected cells. RSV infection of airway epithelial cells resulted in decreased Stat2 expression and function with preservation of upstream signaling events, providing a molecular mechanism for viral inhibition of the type I IFN JAK-STAT pathway. Furthermore, nonspecific pharmacologic inhibition of proteasome function in RSV-infected cells restored Stat2 levels and IFN-dependent activation of Stat1. The results indicate that RSV acts on epithelial cells in the airway to directly modulate the type I IFN JAK-STAT pathway, and this effect is likely mediated though proteasome-dependent degradation of Stat2. Decreased antiviral gene expression in RSV-infected airway epithelial cells may allow RSV replication and establishment of a productive viral infection through subversion of IFN-dependent immunity.

Inflammatory response in airway epithelial cells isolated from patients with cystic fibrosis

The concept that inflammatory gene expression is dysregulated in airway epithelial cells from patients with cystic fibrosis (CF) is controversial. To examine this possibility systematically, responses to inflammatory stimuli were compared in CF airway epithelial cell lines without versus with wild-type CF transmembrane conductance regulator (CFTR) complementation and in tracheobronchial epithelial cells from patients with versus without CF. Epithelial cell expression of the leukocyte adhesion glycoprotein intercellular adhesion molecule-1 (ICAM-1) and release of the neutrophil chemoattractant interleukin (IL)-8 were determined under basal conditions or after exposure to stimuli important in CF airway inflammatory responses. We found that uncorrected CF airway epithelial cell lines inconsistently expressed higher ICAM-1 and IL-8 levels. Human CF tracheobronchial epithelial cells in primary culture released moderately increased IL-8 only after exposure to Pseudomonas aeruginosa. In CF cells with higher IL-8 release, transient expression of wild-type CFTR using an adenoviral vector did not specifically affect cytokine levels. The results indicate that there is considerable variability in airway epithelial cell responses to inflammatory stimuli among different individuals and cell models systems. Although increased ICAM-1 and IL-8 expression are observed in some CF airway epithelial cell models, many CF cells do not exhibit significant dysregulation of these important inflammatory genes.

Inflammatory mediator mRNA expression by adenovirus E1A-transfected bronchial epithelial cells

Lung tissue from patients with emphysema and airway obstruction carries excess adenoviral E1A DNA that is expressed as protein in airway surface epithelium and is associated with an increased inflammatory response. To examine mechanisms by which latent adenoviral infection might amplify the inflammatory process, we transfected primary human bronchial epithelial (HBE) cells from three separate patients undergoing lung resection so that they stably expressed adenovirus E1A. Lipopolysaccharide stimulation of the E1A-transfected HBE cells increased intercellular adhesion molecule-1 and interleukin-8 mRNA and protein expression compared with control cells from the same patient. It also induced greater intercellular adhesion molecule-1 promoter activity and greater nuclear factor-kappa B binding activity of nuclear extracts in E1A transfectants than controls. E1A-positive transfectants constitutively expressed transforming growth factor-beta 1 mRNA and protein, whereas this expression was either very low or not detected in control cells. We conclude that adenoviral E1A transfection transforms primary HBE cells and upregulates their production of mediators that are clinically relevant to the pathogenesis of chronic obstructive pulmonary disease.

Viral induction of a chronic asthma phenotype and genetic segregation from the acute response

Paramyxoviral infections cause most of the acute lower respiratory tract illness in infants and young children and predispose to the development of chronic wheezing, but the relationship between these short- and long-term viral effects are uncertain. Here we show that a single paramyxoviral infection of mice (C57BL6/J strain) not only produces acute bronchiolitis, but also triggers a chronic response with airway hyperreactivity and goblet cell hyperplasia lasting at least a year after complete viral clearance. During the acute response to virus, same-strain ICAM-1-null mice are protected from airway inflammation and hyperreactivity despite similar viral infection rates, but the chronic response proceeds despite ICAM-1 deficiency. Neither response is influenced by IFN-gamma deficiency, but the chronic response is at least partially prevented by glucocorticoid treatment. In contrast to viral infection, allergen challenge caused only short-term expression of asthma phenotypes. Thus, paramyxoviruses cause both acute airway inflammation/hyperreactivity and chronic airway remodeling/hyperreactivity phenotypes (the latter by a hit-and-run strategy, since viral effects persist after clearance). These two phenotypes can be segregated by their dependence on the ICAM-1 gene and so depend on distinct controls that appear critical for the development of lifelong airway diseases such as asthma.

Cell-specific involvement of HNF-1beta in alpha(1)-antitrypsin gene expression in human respiratory epithelial cells

The synergistic action of hepatocyte nuclear factor (HNF)-1alpha and HNF-4 plays an important role in expression of the alpha(1)-antitrypsin (alpha(1)-AT) gene in human hepatic and intestinal epithelial cells. Recent studies have indicated that the alpha(1)-AT gene is also expressed in human pulmonary alveolar epithelial cells, a potentially important local site of the lung antiprotease defense. In this study, we examined the possibility that alpha(1)-AT gene expression in a human pulmonary epithelial cell line H441 was also directed by the synergistic action of HNF-1alpha and HNF-4 and/or by the action of HNF-3, which has been shown to play a dominant role in gene expression in H441 cells. The results show that alpha(1)-AT gene expression in H441 cells is predominantly driven by HNF-1beta, even though HNF-1beta has no effect on alpha(1)-AT gene expression in human hepatic Hep G2 and human intestinal epithelial Caco-2 cell lines. Expression of alpha(1)-AT and HNF-1beta was also demonstrated in primary cultures of human respiratory epithelial cells. HNF-4 has no effect on alpha(1)-AT gene expression in H441 cells, even when it is cotransfected with HNF-1beta or HNF-1alpha. HNF-3 by itself has little effect on alpha(1)-AT gene expression in H441, Hep G2, or Caco-2 cells but tends to have an upregulating effect when cotransfected with HNF-1 in Hep G2 and Caco-2 cells. These results indicate the unique involvement of HNF-1beta in alpha(1)-AT gene expression in a cell line and primary cultures derived from human respiratory epithelium.

Immunity, inflammation, and remodeling in the airway epithelial barrier: epithelial-viral-allergic paradigm

The concept that airway inflammation leads to airway disease has led to a widening search for the types of cellular and molecular interactions responsible for linking the initial stimulus to the final abnormality in airway function. It has not yet been possible to integrate all of this information into a single model for the development of airway inflammation and remodeling, but a useful framework has been based on the behavior of the adaptive immune system. In that paradigm, an exaggeration of T-helper type 2 (Th2) over Th1 responses to allergic and nonallergic stimuli leads to airway inflammatory disease, especially asthma. In this review, we summarize alternative evidence that the innate immune system, typified by actions of airway epithelial cells and macrophages, may also be specially programmed for antiviral defense and abnormally programmed in inflammatory disease. Furthermore, this abnormality may be inducible by paramyxoviral infection and, in the proper genetic background, may persist indefinitely. Taken together, we propose a new model that highlights specific interactions between epithelial, viral, and allergic components and so better explains the basis for airway immunity, inflammation, and remodeling in response to viral infection and the development of long-term disease phenotypes typical of asthma and other hypersecretory airway diseases.

Transient exposure of human bronchial epithelial cells to cytokines leads to persistent increased expression of ICAM-1

Effects of several cytokines on kinetics of Intercellular Adhesion Molecule-1 (ICAM-1) and Vascular Cell Adhesion Molecule-1 (VCAM-1) expression were studied on a bronchial epithelial cell line (BEAS-2B). VCAM-I was neither constitutively expressed on BEAS-2B cells nor induced by Interferon-gamma (IFN-gamma). Tumor Necrosis Factor-alpha (TNF-alpha), Interleukin-1beta (IL-1beta), IFN-alpha, IL-4, IL-6, IL-8 or Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF). ICAM-1 was constitutively expressed on BEAS-2B cells. IFN-gamma and TNF-alpha upregulated ICAM-1 expression on these cells. The functional importance of IFN-gamma plus TNF-a upregulation of ICAM-1 expression on BEAS-2B cells was demonstrated by neutrophil-BEAS-2B cell adhesion assays. Cytokines are rapidly released and cleared in animals. Therefore, transient cytokine(s) exposure might occur on the bronchial mucosa. Brief incubation of BEAS-2B cells with IFN-gamma plus TNF-alpha led initial upregulation of ICAM-1 expression followed by a protracted downregulation. Our findings stress the importance of studying the mechanism(s) controlling the persistent increased expression of ICAM-1 after brief cytokine(s) exposure.

Interleukin 12 p40 production by barrier epithelial cells during airway inflammation

Human airway epithelial cells appear specially programmed for expression of immune response genes implicated in immunity and inflammation. To better determine how this epithelial system operates in vivo, we analyzed its behavior in mouse models that allow for in vitro versus in vivo comparison and genetic modification. Initial comparisons indicated that tumor necrosis factor alpha induction of epithelial intercellular adhesion molecule 1 required sequential induction of interleukin (IL)-12 (p70) and interferon gamma, and unexpectedly localized IL-12 production to airway epithelial cells. Epithelial IL-12 was also inducible during paramyxoviral bronchitis, but in this case, initial IL-12 p70 expression was followed by 75-fold greater expression of IL-12 p40 (as monomer and homodimer). Induction of IL-12 p40 was even further increased in IL-12 p35-deficient mice, and in this case, was associated with increased mortality and epithelial macrophage accumulation. The results placed epithelial cell overgeneration of IL-12 p40 as a key intermediate for virus-inducible inflammation and a candidate for epithelial immune response genes that are abnormally programmed in inflammatory disease. This possibility was further supported when we observed IL-12 p40 overexpression selectively in airway epithelial cells in subjects with asthma and concomitant increases in airway levels of IL-12 p40 (as homodimer) and airway macrophages. Taken together, these results suggest a novel role for epithelial-derived IL-12 p40 in modifying the level of airway inflammation during mucosal defense and disease.

Modification of transepithelial ion transport in human cultured bronchial epithelial cells by interferon-gamma

Human bronchial epithelial cells were treated in vitro with interferon-gamma or tumor necrosis factor-alpha to assess their effect on transepithelial ion transport. Short-circuit current measurements revealed that Na(+) absorption was markedly inhibited by interferon-gamma (10-1,000 U/ml). The cystic fibrosis transmembrane conductance regulator was also downregulated by interferon-gamma as evident at the protein level and by the decrease in the cAMP-dependent current. On the other hand, interferon-gamma caused an increase of the current elicited by apical UTP application, which is due to the activity of Ca(2+)-dependent Cl(-) channels. Tumor necrosis factor-alpha caused few changes in ion transport. Transepithelial fluid transport was measured in normal and cystic fibrosis cells. At rest, both types of cells showed an amiloride-sensitive fluid absorption that was inhibited by interferon-gamma but not by tumor necrosis factor-alpha. Our results show that interferon-gamma alters the transepithelial ion transport of cultured bronchial cells. This effect may change the ion composition and/or volume of periciliary fluid.

Increased CD44 expression in human bronchial epithelial repair after damage or plating at low cell densities

We have investigated the effect of mechanical damage, cell density, and cell-derived soluble mediators on CD44 expression in a model of bronchial epithelial repair. CD44 (all isoforms) and variant-containing isoforms (CD44v3, CD44v6, and CD44v9) were identified with flow cytometry and immunocytochemistry with image analysis. After mechanical damage, CD44 expression increased up to 500 microm from the wound edge and for up to 48 h in two human bronchial epithelium-derived cell lines, 16HBE14o- and NCI-H292. CD44 expression was unchanged by interferon-gamma and increased by <50% by tumor necrosis factor-alpha. To exclude other soluble factors, a Vaseline spacer was used to temporarily divide petri dishes, with cells at high density on one side and those at low density on the other. After the spacer was removed, the cells at low cell density growing in the shared medium expressed up to fourfold higher CD44, although cell proliferation was unchanged. Thus increased CD44 expression at low cell density was not mediated by soluble factors and may reflect functional involvement in cell motility, dedifferentiation, or altered cell-substrate adhesion in epithelial repair.

beta-Adrenergic agonist modulation of monocyte adhesion to airway epithelial cells in vitro

beta-Adrenergic agonists are commonly used in the treatment of obstructive airway diseases and are known to modulate cAMP-dependent processes of airway epithelial cells. However, little is known regarding the ability of cAMP-dependent mechanisms to influence cell-cell interactions within the airway. Thus we investigated the role of the beta-adrenergic agonist isoproterenol in modulating the ability of human bronchial epithelial cells to support the adhesion of THP-1 cells, a monocyte/macrophage cell line, in vitro. We demonstrated that pretreatment of human bronchial epithelial cells (HBECs) with 10 microM isoproterenol or 100 microM salbutamol augments the adhesion of fluorescently labeled THP-1 cells to HBEC monolayers by approximately 40-60%. The increase in THP-1 cell adhesion occurred with 10 min of isoproterenol pretreatment of HBECs and gradually declined but persisted with up to 24 h of isoproterenol exposure. Exposure of THP-1 cells to isoproterenol or salbutamol before the adhesion assays did not result in an increase in adhesion to HBECs, suggesting that the isoproterenol modulation was primarily via changes in epithelial cells. A specific protein kinase A inhibitor, KT-5720, inhibited subsequent isoproterenol augmentation of THP-1 cell adhesion, further supporting the role of cAMP-dependent mechanisms in modulating THP-1 cell adhesion to HBECs.

Inhibitory effects of endogenous and exogenous interferon-gamma on bronchial hyperresponsiveness, allergic inflammation and T-helper 2 cytokines in Brown-Norway rats

Interferon-gamma (IFN-gamma) is an important cytokine involved in the regulation of allergen-induced immune responses. We examined the role of IFN-gamma in a Brown-Norway rat model of bronchial hyperresponsiveness (BHR) and airway eosinophilia, and its effects on the mRNA expression of T helper type 1 (Th1)/Th2 cytokine. Ovalbumin (OA)-sensitized animals were given either exogenous IFN-gamma (105 U/rat over 3 days, intraperitoneally) or anti-IFN-gamma blocking antibody (DB-1 0.3 mg/rat, intravenously) prior to exposure to OA aerosol and were studied 18-24 hr later. In sensitized animals, OA induced significant BHR, accumulation of eosinophils, T lymphocytes and neutrophils in bronchoalveolar lavage (BAL) fluid, and also increased eosinophils and CD8+ T cells in the airways. Exogenous IFN-gamma attenuated allergen-induced BHR (P<0.02, compared with sham-treated animals) together with a significant reduction in eosinophil and neutrophil numbers in BAL fluid (P<0. 005), and eosinophils and CD8+ T cells in airways (P<0.05). By contrast, anti-IFN-gamma antibody increased airway CD4+ T cells and BHR. Using reverse transcriptase-polymerase chain reaction, significant increases in Th2 [interleukin-4 (IL-4), IL-5 and IL-10], and IFN-gamma cytokine mRNA were found in the lungs of sensitized and OA-exposed animals, while exogenous IFN-gamma significantly suppressed IL-4, IL-5 and IL-10 mRNA expression, and anti-IFN-gamma antibody increased IL-4 and IL-5 mRNA expression. These results indicate that Th1 effects, such as those mediated by IFN-gamma, play a down-regulatory role to suppress the Th2 responses associated with allergen-induced BHR and eosinophilic inflammation.

Virus-inducible expression of a host chemokine gene relies on replication-linked mRNA stabilization

Analysis of the host response to viral infection generally has focused on the capacity of viruses to activate or repress transcription of cellular genes, and this approach is also characteristic of work on RNA viruses such as respiratory syncytial virus (RSV). In the present study, it appeared initially that RSV-driven expression of a critical immune regulator, the beta-chemokine RANTES (regulated upon activation, normal T cell expressed and secreted), in primary-culture airway epithelial cells also depended on inducible gene transcription because expression was accompanied by coordinate increases in transcriptional initiation rate and gene promoter activity. However, RSV-driven increases in RANTES gene transcription and promoter activity were small and transient relative to RANTES expression, and they were no different in size and duration than for inactivated RSV that was incapable of fully inducing RANTES expression. These findings suggested that the increase in RANTES gene transcription was not sufficient for inducible expression and that critical regulatory effects occurred at a posttranscriptional level. This type of mechanism for virus-inducible expression of RANTES was established when we found that replicating (but not inactivated) RSV markedly increased RANTES mRNA half-life (from 0.8 to 6.8 h). In addition, RNase protection assays of heterologous promoter/reporter plasmids indicate that basal instability of RANTES mRNA is mediated at least in part by nucleotides 11-389 of the RANTES gene, and this region is also the target for induction by virus. The distinct pathway for production of RANTES (in combination with cytokine-dependent expression of RANTES and related immune-response genes) may more effectively coordinate immune cell interaction with epithelial barrier cells to mediate host defense.

Constitutive activation of an epithelial signal transducer and activator of transcription (STAT) pathway in asthma

Cytokine effects on immunity and inflammation often depend on the transcription factors termed signal transducers and activators of transcription (STATs), so STAT signaling pathways are candidates for influencing inflammatory disease. We reasoned that selective IFN responsiveness of the first STAT family member (Stat1) and Stat1-dependent immune-response genes such as intercellular adhesion molecule-1 (ICAM-1), IFN regulatory factor-1 (IRF-1), and Stat1 itself in airway epithelial cells provides a basis for detecting cytokine signaling abnormalities in inflammatory airway disease. On the basis of nuclear localization and phosphorylation, we found that epithelial Stat1 (but not other control transcription factors) was invariably activated in asthmatic compared with normal control or chronic bronchitis subjects. Furthermore, epithelial levels of activated Stat1 correlated with levels of expression for epithelial ICAM-1, IRF-1, and Stat1, and in turn, ICAM-1 levels correlated with T-cell accumulation in tissue. However, only low levels of IFN-gamma or IFN-gamma-producing cells were detected in airway tissue in all subjects. The results therefore provide initial evidence linking abnormal behavior of STAT pathways for cytokine signaling to the development of an inflammatory disease. In that context, the results also change the current scheme for asthma pathogenesis to one that must include a localized gain in transcriptional signal ordinarily used for a T helper 1-type cytokine (IFN-gamma) in combination with allergy-driven overproduction of T helper 2-type cytokines.

Lymphocyte subsets in distinct lung compartments show a different ability to produce interferon-gamma (IFN-gamma) during a pulmonary immune response

Lymphocytes play an important immunoregulatory role in pulmonary immune responses. By releasing cytokines they can control the cell-cell communication of other participating cells. Although it is well established that the lung lymphocytes, localized in distinct compartments, differ in their subset composition, little is known about cytokine production in these compartments during immune responses. Lewis rats were immunized by intravenous administration of sheep erythrocytes on day 0 and day 7 and challenged intratracheally with sheep erythrocytes on day 10. Four days after intratracheal (i.t.) challenge the composition of lymphocyte subsets (CD2+, CD4+, CD8+, B cells, natural killer (NK) cells) in the spleen, blood, lung perfusate, lung tissue and bronchoalveolar lavage fluid (BALF) was characterized, and intracellular IFN-gamma was detected in these subsets by flow cytometry. Comparing control and immunized animals, no changes were found in lymphocyte numbers, subsets or the percentage of IFN-gamma-producing lymphocytes in the spleen, blood and lung perfusate. In lung tissue and BALF, however, the absolute number of all lymphocyte subsets and the percentage of IFN-gamma-producing lymphocytes were increased. When the lymphocyte subsets were analysed an increased percentage of IFN-gamma-producing T cells was found in lung tissue (4.5 +/- 0.6% versus 12.8 +/- 1.1%) and in BALF (7.8 +/- 1.4% versus 14.8 +/- 1.9%) of immunized animals opposed to controls, this increase being seen in both CD4+ and CD8+ cells. Thus, there is an accumulation of T cells with an increased potential to produce IFN-gamma in the lung interstitium and the bronchoalveolar space during pulmonary immune responses.

Patterns for RANTES secretion and intercellular adhesion molecule 1 expression mediate transepithelial T cell traffic based on analyses in vitro and in vivo

Immune cell migration into and through mucosal barrier sites in general and airway sites in particular is a critical feature of immune and inflammatory responses, but the determinants of transepithelial (unlike transendothelial) immune cell traffic are poorly defined. Accordingly, we used primary culture airway epithelial cells and peripheral blood mononuclear cells to develop a cell monolayer system that allows for apical-to-basal and basal-to-apical T cell transmigration that can be monitored with quantitative immunofluorescence flow cytometry. In this system, T cell adhesion and subsequent transmigration were blocked in both directions by monoclonal antibodies (mAbs) against lymphocyte function-associated antigen 1 (LFA-1) or intercellular adhesion molecule 1 (ICAM-1) (induced by interferon gamma [IFN-gamma] treatment of epithelial cells). The total number of adherent plus transmigrated T cells was also similar in both directions, and this pattern fit with uniform presentation of ICAM-1 along the apical and basolateral cell surfaces. However, the relative number of transmigrated to adherent T cells (i.e., the efficiency of transmigration) was increased in the basal-to-apical relative to the apical-to-basal direction, so an additional mechanism was needed to mediate directional movement towards the apical surface. Screening for epithelial-derived beta-chemokines indicated that IFN-gamma treatment caused selective expression of RANTES (regulated upon activation, normal T cell expressed and secreted), and the functional significance of this finding was demonstrated by inhibition of epithelial-T cell adhesion and transepithelial migration by anti-RANTES mAbs. In addition, we found that epithelial (but not endothelial) cells preferentially secreted RANTES through the apical cell surface thereby establishing a chemical gradient for chemotaxis across the epithelium to a site where they may be retained by high levels of RANTES and apical ICAM-1. These patterns for epithelial presentation of ICAM-1 and secretion of RANTES appear preserved in airway epithelial tissue studied either ex vivo with expression induced by IFN-gamma treatment or in vivo with endogenous expression induced by inflammatory disease (i.e., asthma). Taken together, the results define how the patterns for uniform presentation of ICAM-1 along the cell surface and specific apical sorting of RANTES may serve to mediate the level and directionality of T cell traffic through epithelium (distinct from endothelium) and provide a basis for how this process is precisely coordinated to route immune cells to the mucosal surface and maintain them there under normal and stimulated conditions.

Eosinophils Bind Rhinovirus and Activate Virus-Specific T Cells

Episodes of virus-induced exacerbations of asthma are accompanied by increased eosinophils (EOS) in respiratory secretions and evidence of EOS degranulation. Although rhinoviruses (RV) are the viruses most often implicated in exacerbations of asthma in both children and adults, little is known about the immune response to this group of viruses and, in particular, EOS-RV interactions. To define such interactions, we incubated human rhinovirus type 16 (RV16), a serotype using ICAM-1 as a receptor, with EOS purified from PBMC, and measured EOS-RV binding, EOS-mediated Ag presentation and T cell activation, and EOS cell surface marker expression and superoxide production. Significant RV16 binding occurred to EOS that were pretreated with granulocyte-macrophage CSF, and this binding was inhibited by anti-ICAM-1 mAb. EOS also presented viral Ags to RV16-specific T cells, causing T cell proliferation and secretion of IFN-γ. RV16 induced a significant shift from CD18dim to CD18bright, but did not affect EOS expression of CD54, CD69, or HLA-DR. Finally, RV16 did not induce superoxide production from peripheral blood EOS. These findings suggest that RV16 also binds to airway EOS, which resemble granulocyte-macrophage CSF-treated blood EOS in terms of high expression of ICAM-1. Furthermore, our findings suggest that EOS could participate in RV-induced immune responses through Ag presentation and T cell activation. By activating RV-specific T cells, EOS may play an important role in the initiation of antiviral T cell responses, and these effects could also contribute to enhanced airway inflammation and increased asthma symptoms in susceptible individuals.

Interferon gamma and interleukin 4 stimulate prolonged expression of inducible nitric oxide synthase in human airway epithelium through synthesis of soluble mediators

Human respiratory epithelium expresses inducible nitric oxide synthase (iNOS) continuously in vivo, however mechanisms responsible for maintenance of expression are not known. We show that IFNgamma is sufficient for induction of iNOS in primary human airway epithelial cells (HAEC) in vitro, and IL-4 potentiates IFNgamma-induced iNOS expression in HAEC through stabilization of iNOS mRNA. IFNgamma/IL-4- induced iNOS expression in HAEC was delayed in onset and prolonged with expression up to 1 wk. Removal of overlying culture media resulted in loss of expression, while transfer of conditioned media induced iNOS mRNA in other HAEC. IFNgamma and IL-4 stimulation activated STAT1 and STAT6 in HAEC, but conditioned media transfer to HAEC produced even higher levels of STAT1 activation than achieved by direct addition of cytokines. Although cytokine induction of iNOS was dependent on new protein synthesis, conditioned media induction of iNOS in HAEC was not. Further, removal of overlying culture media from cells at different times after cytokine stimulation demonstrated that mediator synthesis and/or secretion important for induction and maintenance of iNOS occurs early after cytokine stimulation. In conclusion, a combination of IFNgamma/ IL-4, which occurs naturally in the lung epithelial lining fluid, leads to maintenance of iNOS expression in human airway epithelium through production of soluble mediators and stabilization of mRNA.

Interferon gamma induces prostaglandin G/H synthase-2 through an autocrine loop via the epidermal growth factor receptor in human bronchial epithelial cells

The induction of prostaglandin G/H synthase (PGHS; prostaglandin endoperoxide synthase, cyclooxygenase) by proinflammatory cytokines accounts, at least in part, for the altered eicosanoid biosynthesis in inflammatory diseases. In secondary cultures of normal human bronchial epithelial cells (NHBECs), interferon-gamma (IFN-gamma, 10 ng/ml for 24 h) increased the amount of prostaglandin E2 (PGE2) released in response to stimulation with exogenous arachidonic acid (5 microM). The enhanced production of PGE2 reflected the upregulation of PGHS-2 as indicated by enhanced expression of PGHS-2 RNA and increased recovery of PGHS-2 protein in NHBECs. IFN-gamma did not alter the production of PGE2 in A549 cells (a human lung adenocarcinoma cell line) or 6-keto-PGF1alpha in human umbilical vein endothelial cells (HUVECs), although prostaglandin release and/or the expression of PGHS-2 RNA in these cell lines was upregulated by other proinflammatory cytokines. Induction of PGHS-2 RNA in IFN-gamma-treated NHBECs, which peaked at 24 h, suggested the presence of an intermediary substance regulating the expression of PGHS-2. When the binding between the epidermal growth factor (EGF) receptor and its ligands was disrupted by a neutralizing antibody (LA-1), IFN-gamma failed to upregulate the release of PGE2 and the expression of PGHS-2 RNA in NHBECs. Furthermore, IFN-gamma induced the expression of RNAs for a number of ligands at the EGF receptor TGF-alpha; heparin-binding EGF-like growth factor (HB-EGF); and amphiregulin in NHBECs, and when administered exogenously, these ligands increased PGE2 release from NHBECs. Heparin at the concentration that neutralized the function of amphiregulin, or antibodies against TGFalpha or HB-EGF also reduced the release of PGE2 from IFN-gamma-stimulated NHBECs. These data are consistent with the presence of an autocrine growth factor/EGF receptor loop regulating PGHS-2 expression and PGE2 synthesis in bronchial epithelial cells.

Inflammatory infiltration of the upper airway epithelium during Sendai virus infection: involvement of epithelial dendritic cells

We undertook the present study to determine the nature of the cellular inflammatory response within the epithelial lining of the rat trachea during a Sendai virus infection. In particular, we aimed to investigate changes in the resident population of epithelial dendritic cells. Rats were infected with Sendai virus, and tracheal tissue was examined immunohistochemically at various times with a panel of cell-specific monoclonal antibodies. We found that Sendai virus infection was restricted to only the lumenal layer of epithelial cells and that virus nucleoprotein was present from days 2 to 5 postinfection. Starting around day 2 or 3, there was a large cellular influx consisting of macrophages, neutrophils, NK cells, and T cells; this coincided with expression of high levels of ICAM-1 on the basal (uninfected) layers of the epithelium. The T cells were mostly alphabeta T-cell receptor positive; however, a smaller influx of gammadelta T cells also took place. The number of resident dendritic cells increased markedly during infection, with numbers peaking around day 5 and remaining elevated 14 days later. The peak of the inflammatory response occurred on day 5 and declined thereafter, with the exception of dendritic cell and alphabeta T-cell numbers, which remained elevated. Starting around day 3, the tracheal epithelial cells expressed increasing levels of major histocompatibility complex class II antigen. This expression was maximal at day 5 and declined rapidly thereafter. In vitro culture of tracheal segments demonstrated that viral infection was not per se responsible for the upregulation of class II expression and that when cultured in the presence of gamma interferon, class II antigen was induced on epithelial cells.

Bronchial inflammation and the common cold: a comparison of atopic and non-atopic individuals

Background Cold virus infections are associated with asthma attacks and with increased bronchial responsiveness even in normal subjects. Possible mechanisms include epithelial damage, interaction with adhesion molecules or with T‐helper cell subsets.

Objective To determine whether colds increase lower airway inflammation, comparing atopic with non‐atopic normal subjects.

Methods Thirty healthy volunteers (15 atopic) took part. Basehne tests included viral serology. microbiological culture and polymerase chain reaction for rhinovirus infection (HRV‐PCR), histamine bronchial provocation and bronchoscopy. Twenty subjects (eight atopic) underwent repeat tests when they developed a cold.

Results Forced expiratory volume in one second (FEV₁) was significantly lower during colds (‐0.19L [95% confidence mterval ‐0.10, ‐0.29], P= 0,0004) and there was a significant increase in bronchial responsiveness (+0.62 doublings of the dose‐response slope [+0.24, +1.00], P=0.003). Eight subjects (two atopic) had a diagnosed viral infection: two HRV. three coronavirus (HCV), one HRV + HCV, one parainfluenza III(PI) and one respiratory syncytial virus (RSV) (also Haemophilus influenzae). In biopsies, during colds, total eosinophils (EG1⁺) increased significantly (geometric mean 6.73‐fold [1.12,40.46], P=O.04). Activated eosinophils (EG2⁺) only increased significantly in the subgroup without diagnosed viral infection and particularly in atopic rhinitics. T‐suppressor (CD8⁺) cells also increased significantly (median +178.3 cells mm², P= 0.004). Epithelial expression of intercellular adhesion molecule‐1 (ICAM‐1) expression increased in four atopic rhinitics during colds. Bronchial washings showed a significant increase in neutrophils (GM 1.53‐fold [1.04,2.25], P= 0.02).

Conclusion Lower airway inflammation was present in atopic and non‐atopic normal subjects with colds. Atopic subjects differed in that they were less likely to have positive virological tests and were more likely to show activated eosinophilia in the lower airway, despite a similar spectrum of symptoms.

Tumour necrosis factor-alpha-induced ICAM-1 expression in human vascular endothelial and lung epithelial cells: modulation by tyrosine kinase inhibitors

1. Tumour necrosis factor-alpha (TNF alpha) increases the expression of the adhesion molecule intercellular adhesion molecule-1 (ICAM-1) on cultured endothelial and epithelial cells and modulation of this may be important in controlling inflammation. Activation of tyrosine kinase(s) is known to be involved in the signal transduction pathways of many cytokines. In this study we have investigated the effects of the tyrosine kinase inhibitors, ST638, tyrphostin AG 1288 and genistein, on TNF alpha-induced ICAM-1 expression in human alveolar epithelial (A549) and vascular endothelial (EAhy926) cell lines and also normal human lung microvascular endothelial cells (HLMVEC). 2. ICAM-1 expression on cultured cells was determined by a sensitive enzyme-linked immunosorbant assay (ELISA). Endothelial or epithelial monolayers were exposed to increasing doses of TNF-alpha (0.01-10 ng ml-1), in the presence or absence of either ST638 (3-100 microM), AG 1288 (3-100 microM) or genistein (100 microM) and ICAM-1 expression was measured at 4 and 24 h. Control experiments examined the effect of ST638 on phorbol 12-myristate 13-acetate (PMA, 20 ng ml-1, 4 h)-stimulated ICAM-1 and compared it to that of a specific protein kinase C inhibitor, R031-8220 (10 microM). Also, functional consequences of changes in ICAM-1 expression were assessed by measuring adhesion of 111 In-labelled human neutrophils to EAhy926 endothelial and A549 epithelial monolayers treated with TNF alpha, in the presence or absence of ST638. 3. ST638 caused a concentration-dependent reduction in TNF alpha- (0.1-10 ng ml-1)-induced ICAM-1 on EAhy926 endothelial (at 4 h) and A549 epithelial monolayers (at 4 and 24 h). In contrast, ST638 caused a concentration-dependent increase in TNF alpha- (0.1-10 ng ml-1)-induced ICAM-1 on EAhy926 endothelial cells at 24 h. Similar effects were seen with AG 1288 or genistein. ST638 (100 microM) significantly (P < 0.01) inhibited ICAM-1 expression on HLMVEC endothelial cells induced by 0.01 ng ml-1 TNF alpha at 4 or 24 h or 0.1 ng ml-1 at 4 h, but increased ICAM-1 expression induced by 0.1 ng ml-1 TNF alpha at 24 h. ST638 did not significantly change the expression of PMA-stimulated ICAM-1 on either A549 epithelial, EAhy926 or HLMVEC endothelial cells. However, PMA-induced ICAM-1 expression was inhibited by Ro31-8220. Also, treatment of epithelial or endothelial monolayers with TNF alpha and ST638 altered adhesion of human neutrophils to A549 epithelial or EAhy926 endothelial cells in a manner that corresponded to the alteration in ICAM-1 expression. 4. These results show that tyrosine kinase inhibitors alter TNF alpha-induced ICAM-1 expression, but that the cell type, concentration of TNF alpha and time of exposure to this cytokine determine whether expression is decreased or increased by the inhibitor. An increased understanding of the signal transduction pathway(s) involved in TNF alpha-induced ICAM-1 expression on lung epithelial and vascular endothelial cells may be of potential therapeutic value in the treatment of inflammatory disease.

Blood eosinophil counts and arterial oxygen tension in acute asthma

OBJECTIVE

To investigate whether during acute asthma episodes a decrease in blood eosinophil count could correlate with the severity of the disease.

DESIGN

Prospective study on paediatric asthmatic patients admitted for acute asthma exacerbation between January 1992 and August 1993. All patients were regularly followed up in an outpatient clinic and had had a complete clinical evaluation < 1 month before admission.

SETTING

Pulmonary division of the G Gaslini paediatric research institute, Genoa, Italy.

SUBJECTS

21 asthmatic patients, 59 (SEM 9) months of age, admitted for acute asthma exacerbation. On the basis of clinical evaluation and the results of blood and microbiological tests performed during acute asthma exacerbations, patients were divided into two subgroups: infected (n = 13) and non-infected (n = 8).

RESULTS

All but one of the patients showed a marked decrease in blood eosinophil count during the acute asthma episode, in comparison with recent count (< 1 month before admission) obtained in clinically stable conditions: 662 (116) v 210 (54) eosinophils/mm3, p < 0.0003. The decrease in the eosinophil count was more pronounced in the infected patients than in the non-infected patients, but the difference was not statistically significant (p > 0.05). Similarly, transcutaneous arterial oxygen pressure (PaO2) values measured during acute asthma exacerbations tended to be lower in infected patients, without, however, reaching statistical significance: 8.6 (0.7) v 10.1 (0.9) kPa, p > 0.05). The correlation between the decrease in blood eosinophil count and PaO2 during the acute asthma exacerbations was significant in all the patients (r2 = 0.235, p = 0.022) and in the non-infected patients (r2 = 0.653, p = 0.015), but not in infected patients. In this latter subgroup, a significant negative correlation was found between blood neutrophil counts during acute asthma exacerbations and PaO2 (r2 = 349, p = 0.026).

CONCLUSIONS

During acute asthma exacerbations in atopic patients without clinical evidence of infection, the decrease in blood eosinophil count correlates significantly with the decrease in PaO2, further supporting the role of eosinophils in allergic asthma.