Quantitation of eosinophil Major Basic Protein cytotoxicity to rodent respiratory epithelium

Reovirus type-2 infection in newborn DBA/1J mice reduces the development of late allergic asthma

The aim of the present study was to determine whether or not the development of a helper T (Th) 1 response induced by Reovirus type-2 (Reo-2) infection would protect against the development of Th2-mediated late allergic asthma. This hypothesis was examined by infecting one day old neonatal DB A/1J mice with Reo-2 in an ovalbumin (OVA)-induced late asthma model. Compared with the controls (either infected or uninfected mice with or without OVA sensitization and/or OVA challenge), Reo-2 infection lessened the magnitude of the subsequent allergic Th2-mediated late asthma. In infected mice with allergic late asthma, there was decreased infiltration of interleukin (IL)-4(+), IL-5(+), IL-13(+) and very late antigen (VLA)-4(+) lymphocytes, and eotaxin-2(+) and VLA-4(+) eosinophils, in both bronchial and bronchiolar lesions. Also the expression of vascular cell adhesion molecule (VCAM)-1 and eotaxin-2 on vascular endothelial cells was reduced. Moreover, the systemic production of IL-4, IL-5, tumour necrosis factor-α and OVA-specific IgE was reduced, whereas systemic IFN-γ production was increased. In addition, there was no increase in IFN-α production. Thus the present study suggests that systemic Reo-2 infection at birth may reduce the development of subsequent late allergic asthma by the induction of a Th1 response. Therefore the potential suppressive mechanism(s) that might be induced by Reo-2 infection in newborn mice and their effects on the development of late allergic asthma are discussed.

Eosinophil-derived cationic proteins activate the synthesis of remodeling factors by airway epithelial cells

Eosinophil cationic proteins influence several biological functions of the respiratory epithelium, yet their direct contribution to airway remodeling has not been established. We show that incubation of the human bronchial epithelial cell line, BEAS-2B, or primary cultured human bronchial epithelial cells, normal human bronchial epithelial cells, with subcytotoxic concentrations (0.1, 0.3, and 1 microM) of major basic protein (MBP), or eosinophil peroxidase (EPO), augmented the transcripts of endothelin-1, TGF-alpha, TGF-beta1, platelet-derived growth factor (PDGF)-beta, epidermal growth factor receptor, metalloproteinase (MMP)-9, fibronectin, and tenascin. A down-regulation of MMP-1 gene expression was observed exclusively in BEAS-2B cells. Cationic protein-induced transcriptional effects were followed by the release of endothelin-1, PDGF-AB in the supernatants by ELISA, and by a down- and up-regulation, respectively, in the levels of MMP-1 and MMP-9 in cell lysates, by Western blot. Cell stimulation with the synthetic polycation, poly-L-arginine, reproduced some but not all effects of MBP and EPO. Finally, simultaneous cell incubation with the polyanion molecules, poly-L-glutamic acid or heparin, restored MMP-1 gene expression but incompletely inhibited MBP- and EPO-induced transcriptional effects as well as endothelin-1 and PDGF-AB release, suggesting that cationic proteins act partially through their cationic charge. We conclude that eosinophil-derived cationic proteins are able to stimulate bronchial epithelium to synthesize factors that influence the number and behavior of structural cells and modify extracellular matrix composition and turnover.

Improved Ventricular Function during Inhalation of PGI2 Aerosol Partly Relies on Enhanced Myocardial Contractility

Inhaled prostacyclin (PGI(2)) aerosol induces selective pulmonary vasodilation. Further, it improves right ventricular (RV) function, which may largely rely on pulmonary vasodilation, but also on enhanced myocardial contractility. We investigated the effects of the inhaled PGI(2) analogs epoprostenol (EPO) and iloprost (ILO) on RV function and myocardial contractility in 9 anesthetized pigs receiving aerosolized EPO (25 and 50 ng.kg(-1).min(-1)) and, consecutively, ILO (60 ng.kg(-1).min(-1)) for 20 min each. We measured pulmonary artery pressure (PAP), RV ejection fraction (RVEF) and RV end-diastolic-volume (RV-EDV), and left ventricular end-systolic pressure-volume-relation (end-systolic elastance, E(es)). EPO and ILO reduced PAP, increased RVEF and reduced RVEDV. E(es) was enhanced during all doses tested, which reached statistical significance during EPO(25 ng) and ILO, but not during EPO(50 ng). PGI(2) aerosol enhances myocardial contractility in healthy pigs, contributing to improve RV function.

Allergen-induced eosinophil cytolysis is a primary mechanism for granule protein release in human upper airways

Cytotoxic eosinophil granule proteins are considered important in the pathogenesis of allergic airway diseases such as rhinitis and asthma. To explore the cellular mechanisms behind eosinophil granule release in human allergic airways, 16 symptom-free patients with seasonal allergic rhinitis were challenged daily with allergen during 1 wk. Nasal lavage samples and biopsies, obtained before and 24 h after the last allergen exposure, were processed for immunohistochemical and electron microscopic analysis. The allergen challenges produced nasal symptoms, marked tissue eosinophilia, and an increase in lavage fluid levels of eosinophil cationic protein (ECP). The nasal mucosa areas with intense extracellular immunoreactivity for ECP were associated with abundant free eosinophil granules. Electron microscopy confirmed the free granules and revealed that all mucosal eosinophils were involved in granule release, either by cytolysis (33%) or piecemeal degranulation (PMD) (67%). Resting or apoptotic eosinophils were not observed. Cytolytic eosinophils had less signs of intracellular granule release (p < 0. 001) and a higher content of intact granules (p < 0.001) compared with viable eosinophils in the same tissue. This study demonstrates eosinophil cytolysis (ECL) as a distinct mechanism for granule mediator release in human allergic airway mucosa. The nature and extent of the ECL and its product (i.e., protein-laden extracellular granules) indicate that allergen-induced cytolysis is a primary and major mechanism for the release of eosinophil proteins in human allergic airway inflammation in vivo.

Eosinophil major basic protein increases membrane permeability in mammalian urinary bladder epithelium

The eosinophil granule protein major basic protein (MBP) is toxic to a wide variety of cell types, by a poorly understood mechanism. To determine whether the action of MBP involves an alteration in membrane permeability, we tested purified MBP on rabbit urinary bladder epithelium using transepithelial voltage-clamp techniques. Addition of nanomolar concentrations of MBP to the mucosal solution caused an increase in apical membrane conductance only when the voltage across the apical membrane was cell interior negative. The magnitude of the MBP-induced conductance was a function of MBP concentration, and the rate of the initial increase in conductance was a function of the transepithelial voltage. The MBP-induced conductance was nonselective for K+ and Cl-. Mucosal Ca2+ reversed the induced conductance, whereas mucosal Mg2+ partially blocked the induced conductance and slowed the rate of the increase in conductance. The induced conductance was partially reversed by changing the voltage gradient across the apical membrane to cell interior positive. Prolonged exposure resulted in an irreversible loss of the barrier function of the urinary bladder epithelium. These results suggest that an increase in cell membrane ion permeability is an initial step in MBP-induced loss of barrier function.