Kazutoshi Yamaguchi

Allergic airway hyperresponsiveness, inflammation, and remodeling do not develop in phosphoinositide 3-kinase γ–deficient mice

BACKGROUND Bronchial asthma is characterized by chronic airway inflammation caused by inflammatory cells. Phosphoinositide 3-kinases (PI3Ks) are known to play a prominent role in fundamental cellular responses of various inflammatory cells, including proliferation, differentiation, and cell migration. PI3Ks therefore are expected to have therapeutic potential for asthma. Although some investigations of the involvement between the pathogenesis of asthma and PI3K have been performed, it is unknown whether PI3Kgamma, a PI3K isoform, is involved in the pathogenesis of asthma. OBJECTIVE We investigated the role of PI3Kgamma in allergen-induced allergic airway inflammation, airway hyperresponsiveness (AHR), and airway remodeling with PI3Kgamma-deficient mice. METHODS After ovalbumin (OVA) sensitization, wild-type (WT) and PI3Kgamma-deficient mice were exposed to aerosolized OVA 3 days per week for 5 weeks. RESULTS In OVA-sensitized and OVA-challenged (OVA/OVA) PI3Kgamma-deficient mice, levels of airway inflammation, AHR, and airway remodeling were significantly decreased compared with those in OVA/OVA WT mice. On the other hand, no significant differences were detected in serum OVA-specific IgE and IgG1 levels and CD4/CD8 balance in bronchoalveolar lavage fluid between OVA/OVA WT mice and OVA/OVA PI3Kgamma-deficient mice. To determine in which phase of allergic responses PI3Kgamma plays a role, we transferred splenocytes from OVA-sensitized WT or PI3Kgamma-deficient mice to naive mice of either genotype. Similar increased levels of eosinophils were induced in both WT recipient mice but not in both PI3Kgamma-deficient recipient mice. CONCLUSION PI3Kgamma might be involved in allergic airway inflammation, AHR, and airway remodeling by regulating the challenge/effector phase of allergic responses.

Hepatocyte growth factor attenuates eotaxin and PGD2-induced chemotaxis of human eosinophils

Background:  Hepatocyte growth factor (HGF) is known to influence a number of cell types, and regulate various biologic activities including cell migration, proliferation, and survival. In a recent study, we found that, in vivo, HGF suppresses allergic airway inflammation, i.e. the infiltration of inflammatory cells including eosinophils into the airway, and further, that HGF reduces Th2 cytokine levels; however, the directly physiologic role of HGF with eosinophils remains unclear. In this study, we investigate the potential of recombinant HGF to regulate the factor‐induced chemotaxis of human eosinophils.

The Synthetic PPARγ Agonist Troglitazone Inhibits IL-5-Induced CD69 Upregulation and Eosinophil-Derived Neurotoxin Release from Eosinophils

Peroxisome proliferator-activated receptor-γ (PPARγ) is a nuclear receptor that regulates lipid metabolism. Recently, PPARγ was reported to be a negative regulator in the immune system. Eosinophils also express PPARγ, however, the role of PPARγ in eosinophil functions is not well understood. Surface expression of CD69 and eosinophil-derived neurotoxin (EDN) release are well-known activation markers of eosinophils. We investigated the effect of a PPARγ agonist on human eosinophil functions such as IL-5-induced CD69 surface expression and EDN release. IL-5 significantly induced eosinophil CD69 surface expression analyzed using flow cytometry and EDN release measured by ELISA. IL-5-induced eosinophil CD69 surface expression and EDN release were significantly inhibited by the synthetic PPARγ agonist troglitazone, and these effects were reversed by a PPARγ antagonist. The PPARγ agonist troglitazone has a potent inhibitory effect on activation and degranulation of eosinophils, and it may be a therapeutic modality for the treatment of allergic diseases.

Anti-Allergic Inflammatory Effects of Hepatocyte Growth Factor

Hepatocyte growth factor (HGF) is known to influence a number of cell types and regulate various biological activities including cytokine production, cell migration, proliferation and survival. Thus, HGF is now recognized to be a key factor in the prevention and attenuation of disease progression. We have reported that HGF reduces allergic airway inflammation, airway hyperresponsiveness, remodeling and development of Th2 cytokines as well as growth factors such as transforming growth factor-β in vivo. In vitro, HGF directly attenuates chemotaxis of eosinophils in the absence of Th2 cytokines and modulates mitogen-activated protein kinases, which play an important role in eosinophil migration. In this review, we discuss the physiological role of HGF in allergic inflammation and its mechanism of anti-inflammatory effects, including the regulation of eosinophil functions.

Possible novel receptor for PGD2 on human bronchial epithelial cells.

Prostaglandin D2 (PGD2), a major prostanoid produced by activated mast cells, has long been implicated in allergic diseases. Recent studies have shown that PGD2 exerts its effects through two different G-protein-coupled receptors (GPCRs), the D-prostanoid receptor (DP) and the chemoattractant receptor-homologous molecule expressed on T helper type-2 cells (CRTH2), expressed in various human tissues. The PGD2/CRTH2 system mediates the chemotaxis of eosinophils, basophils, and Th2 cells, which are involved in the induction of allergic inflammation. We have reported that normal human bronchial epithelial cells (NHBE) and epithelial cell lines (NCI-H292) expressed CRTH2, and PGD2 induces production of IL-8 and GM-CSF. This review discusses the role of CRTH2/DP on epithelial cells and mentions a possible novel receptor for PGD2.

Original article: Hepatocyte growth factor attenuates eotaxin and PGD2‐induced chemotaxis of human eosinophils

Background:  Hepatocyte growth factor (HGF) is known to influence a number of cell types, and regulate various biologic activities including cell migration, proliferation, and survival. In a recent study, we found that, in vivo, HGF suppresses allergic airway inflammation, i.e. the infiltration of inflammatory cells including eosinophils into the airway, and further, that HGF reduces Th2 cytokine levels; however, the directly physiologic role of HGF with eosinophils remains unclear. In this study, we investigate the potential of recombinant HGF to regulate the factor‐induced chemotaxis of human eosinophils.

Effect of Ketotifen on the Production of Reactive Oxygen Species from Human Eosinophils Primed by Eotaxin

Ketotifen is an antiallergic drug and may have direct inhibitory effects on eosinophils. To investigate the anti-eosinophilic effect of ketotifen, we examined the effect of ketotifen on the production of reactive oxygen species (ROS) from eotaxin-primed human eosinophils. Ketotifen at 10–10–10–6 mol/l significantly reduced the production of ROS evoked by A23187 from eosinophils primed by eotaxin. In contrast, ketotifen at 10–5 mol/l significantly augmented the production in the absence of eotaxin. We demonstrated that appropriate concentrations of ketotifen may have direct inhibitory effects on eosinophil oxidative metabolism primed by eotaxin. Ketotifen may contribute to the treatment of allergic disease through its anti-eosinophilic effects.

Red blood cells regulate eosinophil chemotaxis by scavenging RANTES secreted from endothelial cells

Background Eosinophils play a critical role in the pathogenesis of allergic diseases. CC chemokines, such as regulated on activation, normal, T cell expressed, and secreted (RANTES), are key regulators of eosinophil locomotion. Although eosinophils migrate from the bloodstream into tissues, mechanisms that generate a chemogradient across the endothelium remain to be fully elucidated.

Effect of Roxithromycin on Eotaxin-Primed Reactive Oxygen Species from Eosinophils

Background: The CC chemokine eotaxin not only attracts eosinophils to inflamed sites but also promotes adhesion, degranulation and reactive oxygen species production of eosinophils. Reactive oxygen species released from eosinophils are believed to injure epithelial cells at inflamed sites, resulting in airway hyperresponsiveness. Roxithromycin has been reported to have antiasthmatic effects, although its mechanism of action is not thoroughly understood. Therefore, the effect of roxithromycin on eotaxin-primed reactive oxygen species production from eosinophils was studied. Methods: Reactive oxygen species production by eosinophils cultured with or without roxithromycin was evaluted using luminol-dependnet chemiluminescence. Results: Roxithromycin inhibited the release of reactive oxygen species from eosinophils evoked with the calcium ionophore A23187, regardless of pretreatment with or without eotaxin. Conclusion: Roxithromycin may protect epithelial cells at inflamed sites, at least partly by inhibiting the release of reactive oxygen species from eosinophils.

Hepatocyte Growth Factor Suppresses Production of Reactive Oxygen Species and Release of Eosinophil-Derived Neurotoxin from Human Eosinophils

Background:Reactive oxygen species (ROS) and eosinophilic granule proteins such as eosinophil-derived neurotoxin (EDN) are known to damage bronchial tissue and cause airway hyperresponsiveness (AHR) in asthma. Hepatocyte growth factor (HGF) regulates various biological activities and is known to be a multifunctional factor. In our previous study, we found that HGF suppressed allergic airway inflammation and AHR in a murine model of asthma. However, there have been few reports regarding the detailed mechanism of the anti-allergic effect of HGF in asthma. In this study, we investigated the potential of recombinant HGF to regulate the production of ROS and the release of EDN from human eosinophils. Methods:Eosinophils were isolated from subjects with mild eosinophilia by modified CD16-negative selection. We investigated the expression of CD69, an activation marker of eosinophils, on eosinophils, using flow cytometry. Further, ROS production from eosinophils was analyzed using luminol-dependent chemiluminescence, and EDN release was measured by ELISA. Results:Treatment with HGF suppressed interleukin-5-induced upregulation of CD69 expression, ROS production and EDN release from human eosinophils. Conclusion:Taken together, these data suggest that in asthma, HGF attenuates allergic airway inflammation and AHR through at least the suppression of ROS production and EDN release from eosinophils.