Abstract
BackgroundAirway eosinophilia is considered a central event in the pathogenesis of asthma. The toxic components of eosinophils are thought to be important in inducing bronchial mucosal injury and dysfunction. Previous studies have suggested an interaction between nitric oxide (NO) and chemokines in modulating eosinophil functions, but this is still conflicting. In the present study, we have carried out functional assays (adhesion and degranulation) and flow cytometry analysis of adhesion molecules (VLA-4 and Mac-1 expression) to evaluate the interactions between NO and CC-chemokines (eotaxin and RANTES) in human eosinophils.MethodsEosinophils were purified using a percoll gradient followed by immunomagnetic cell separator. Cell adhesion and degranulation were evaluated by measuring eosinophil peroxidase (EPO) activity, whereas expression of Mac-1 and VLA-4 was detected using flow cytometry.ResultsAt 4 h incubation, both eotaxin (100 ng/ml) and RANTES (1000 ng/ml) increased by 133% and 131% eosinophil adhesion, respectively. L-NAME alone (but not D-NAME) also increased the eosinophil adhesion, but the co-incubation of L-NAME with eotaxin or RANTES did not further affect the increased adhesion seen with chemokines alone. In addition, L-NAME alone (but not D-NAME) caused a significant cell degranulation, but it did not affect the CC-chemokine-induced cell degranulation. Incubation of eosinophils with eotaxin or RANTES, in absence or presence of L-NAME, did not affect the expression of VLA-4 and Mac-1 on eosinophil surface. Eotaxin and RANTES (100 ng/ml each) also failed to elevate the cyclic GMP levels above baseline in human eosinophils.ConclusionEotaxin and RANTES increase the eosinophil adhesion to fibronectin-coated plates and promote cell degranulation by NO-independent mechanisms. The failure of CC-chemokines to affect VLA-4 and Mac-1 expression suggests that changes in integrin function (avidity or affinity) are rather involved in the enhanced adhesion.
Highlights
Airway eosinophilia is considered a central event in the pathogenesis of asthma
The integrin VLA-4 is constitutively expressed in eosinophils [5], whereas Mac-1 is expressed in eosinophils stimulated with different class of mediators such as platelet-activating factor (PAF), granulocyte macrophage colony stimulating factor (GM-CSF), and N-formyl-methionyl-leucyl-phenylalanine [68]
At 2 and 3 h incubation, neither eotaxin nor RANTES significantly increased the eosinophil adhesion to fibronectin in comparison with non-stimulated cells
Summary
Airway eosinophilia is considered a central event in the pathogenesis of asthma. The toxic components of eosinophils are thought to be important in inducing bronchial mucosal injury and dysfunction. The integrin VLA-4 is constitutively expressed in eosinophils [5], whereas Mac-1 is expressed in eosinophils stimulated with different class of mediators such as platelet-activating factor (PAF), granulocyte macrophage colony stimulating factor (GM-CSF), and N-formyl-methionyl-leucyl-phenylalanine (fMLP) [68]. Both Mac-1 and VLA-4 integrins have a role in the degranulation and superoxide anion production in stimulated eosinophils [6,9], and can be referred as mediators of eosinophil functions. Eosinophils bind to CS-1 with high avidity, an effect inhibited with neutralizing antibodies to α4 integrins expressed by eosinophils or with neutralizing antibodies to CS-1 [11]
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