The role of eosinophils in asthma

p-STAT6, PU.1, and NF-κB are involved in allergen-induced late-phase airway inflammation in asthma patients

Background

Previous in vitro and animal studies demonstrated that transcription factors p-STAT6 and PU.1 are required to induce interleukin (IL)-9 secretion by T helper (Th) 9 cells. It is believed that n factor-kappaB (NF-κB) plays a role in eosinophil survival. The importance of these transcription factors in the pathogenesis of allergic asthma (AA) in humans is poorly understood. We evaluated p-STAT6 and PU.1 expression in peripheral blood Th9 cells and NF-κB expression in eosinophils during late-phase airway inflammation in AA patients.

Methods

Nineteen adults with AA and 14 adult healthy individuals (HI) were examined. Peripheral blood collected 24 h before (baseline) and 24 h after bronchial allergen challenge. CD4⁺ cells and eosinophils were isolated by high-density gradient centrifugation and magnetic separation. The percentage of Th9 cells and apoptotic eosinophils was estimated by flow cytometry. p-STAT6 and PU.1 expression was expressed as mean fluorescence intensity (MFI) in Th9 cells. NF-κB levels were expressed as MFI in peripheral blood eosinophils. Serum IL-9 and IL-5 levels were determined by enzyme-linked immunosorbent assay.

Results

At baseline, MFI of p-STAT6 and PU.1 in peripheral blood Th9 cells and MFI of NF-κB in eosinophils and, serum IL-5 and IL-9 levels were greater in AA patients (P < 0.05). Decreased eosinophil apoptosis was seen in the AA group compared with HI (P < 0.05). MFI of p-STAT6, PU.1, and NF-κB and serum levels of IL-5 and IL-9 were increased in the AA group 24 h after challenge compared with baseline (P < 0.05). In the AA group, a correlation between serum IL-9 and Th9 cells (r = 0.7, P = 0.001) and MFI of PU.1 (r = 0.6, P = 0.01) 24 h after bronchial allergen challenge was observed. A correlation between Th9 cells and MFI of p-STAT6 (r = 0.45, P = 0.03) as well as MFI of PU.1 (r = 0.5, P = 0.02) 24 h after challenge was only observed in AA patients. A correlation between the MFI of NF-κB and eosinophil apoptosis was observed in AA patients 24 h before (r = −0.46, P = 0.02) and after (r = −0.5, P = 0.02) challenge.

Discussions

p-STAT6 and PU.1 may be associated with Th9 cells and IL-9 production, whereas NF-κB and IL-5 may be associated with reduced eosinophil apoptosis in allergen-induced late-phase airway inflammation.

Trial registration

ClinicalTrials.gov NCT02214303

Electronic supplementary material

The online version of this article (doi:10.1186/s12890-015-0119-7) contains supplementary material, which is available to authorized users.

Selective inflammatory response induced by intratracheal and intravenous administration of poly-L-arginine in guinea pig lungs

Major basic protein (MBP) is a cationic protein found in eosinophil granules that was postulated to participate in the pathogenesis of bronchial asthma. Recently, it has been demonstrated that MBP level in serum or bronchoalveolar lavage (BAL) fluid was correlated with bronchial hyperresponsiveness (BHR) in asthmatics. A number a studies have established that MBP actions could be mimicked by synthetic polycations as poly-L-arginine. In this study, we investigated the effects of intratracheal and intravenous administration of poly-L-arginine on lung inflammatory response development. The intratracheal injection of poly-L-arginine at the doses of 1, 10, 100 nmol/animal increased the number of eosinophils (up to 3.2 fold) and neutrophils (up to 12 fold) in BAL fluid. Eosinophil and neutrophil infiltration was reversed by 88% and 67% respectively following low molecular weight heparin treatment (500 microg/animal). The intravenous injection of increasing doses of poly-L-arginine (1, 10, 100, 500 nmol/animal) increased the number of eosinophils (up to 2.7 fold) but not neutrophil infiltration in guinea pig lungs. Eosinophil infiltration was reversed by 87% following low molecular weight heparin treatment (1.5 mg/animal). Intratracheal treatment with poly-L-arginine (100 nmol/animal) produced an important increase of beta-glucuronidase, histamine, eosinophil peroxidase (EPO) and albumin levels in BAL fluid, whereas the intravenous treatment (500 nmol/animal) did not. These results show that the route of administration of poly-L-arginine greatly influences its effect on inflammatory cell recruitment since both administration routes elicited eosinophil migration but only the intratracheal route stimulated the migration of neutrophils. Moreover, poly-L-arginine appeared to induce other inflammatory responses since it increased beta-glucuronidase, histamine, EPO and albumin levels in BAL fluid following intratracheal treatment. These results also showed that low molecular weight heparin significantly blocks the inflammatory responses elicited by poly-L-arginine.

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

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

IL-4 induces neutrophilic maturation of HL-60 cells and activation of human peripheral blood neutrophils

IL-4 is a T-helper cell derived cytokine that has effects on myelomonocytic cell maturation and activation. We have studied the effect of IL-4 on neutrophilic maturation using the cell line HL-60 and found that it has a profound effect on the maturation and activation of the cell line. The treatment of HL-60 cells with recombinant hu IL-4 (0.15 to 15.0 ng/ml) induced a shift in the percentage of HL-60 cells staining positive for chloroacetate esterase enzyme activity (indicating commitment to the neutrophilic lineage). IL-4 increased surface expression of the neutrophil-lineage antigen WEM G11, the complement receptors CR3 (CD11b) and CR1 (CD35), but not for the monocyte differentiation antigen CD14. IL-4 treated HL-60 cells demonstrated enhanced Fc- and complement-mediated phagocytic capacity and increased hexose-monophosphate shunt activity. In addition, IL-4 was capable of sustaining the neutrophil maturation of HL-60 cells that had been pre-treated for 24 h with DMSO. To investigate the effect of IL-4 on the mature neutrophil, we studied freshly isolated and rested human peripheral blood neutrophils. In the absence of other stimuli, neutrophils were induced by IL-4 to have significantly elevated phagocytic responses. The response was specific since treatment with anti-human IL-4 abolished phagocytic stimulation. Finally, IL-4 treatment also stimulated resting neutrophils to migrate toward zymosan-activated serum (ZAS) and human IL-5. The results demonstrate that IL-4 is a potent maturation factor for myelocytes to become neutrophils and that IL-4 can stimulate resting mature neutrophils.

Leukotriene B4 induced steady state calcium rise and superoxide anion generation in guinea pig eosinophils are not related events

We have examined the nature of the leukotriene B4 (LTB4) induced steady state intracellular calcium rise [Ca++]i in guinea pig eosinophils and the relationship between LTB4 induced [Ca++]i and superoxide anion (O2-). LTB4 induced a rise in intracellular Ca++ (following a Ca(++)- transient) in a dose dependent manner with an optimal increase around 50-100 nM. Depolarizing concentrations of K+ did not induce [Ca++]i in eosinophils nor did the voltage operated calcium channel inhibitor, nifedipine, inhibit the LTB4 induced Ca++ entry. In contrast, SK&F 96365 a purported receptor operated calcium channel (ROCC) inhibitor, and its parent compound SC 32849, attenuated LTB4 induced [Ca++]i. Five reference anti-asthmatics (ketotifen, formoterol, disodium-cromoglycate, theophylline and budesonide) had no influence on LTB4 induced [Ca++]i. LTB4 also induced O2- generation (a functional response) in a dose dependent manner with optimal effect around 100 nM. However, in contrast to Ca(++)- influx, LTB4 induced O2- generation was not affected by either SK&F 96365 or its analogues or reference anti-asthmatics. The results of this study suggest a) the presence of a non-voltage gated, receptor operated, calcium sequestration process in guinea pig eosinophils, b) that LTB4 induced [Ca++]i and O2- generation are apparently unrelated events in these cells, and c) that standard anti-asthmatics do not have an influence on either LTB4 induced [Ca++]i or O2- generation in these cells.

Future developments in the pharmacotherapy of lung disease

Future advances in the pharmacotherapy of lung disease will occur mainly in the treatment of asthma, and will include the development of new long-acting beta 2-agonists, long-acting parasympatholytics, phosphodiesterase inhibitors, corticosteroids with fewer systemic side-effects, and other antiinflammatory drugs. Free radicals play an important role in most lung diseases, including asthma, emphysema, fibrosis, and adult respiratory distress syndrome. The search for free radical scavengers is now in progress. Replacement therapy with alpha 1-antitrypsin and surfactant is now possible. Progress in this area stems principally from a better understanding of the pathogenesis of lung disease.